Benefits, Disadvantages, and Challenges of Respiratory Gating

UNIVERSITY OF WISCONSIN-LA CROSSE

Graduate Studies

BENEFITS, DISADVANTAGES, AND CHALLENGES OF RESPIRATORY GATING USED

TO TREAT LEFT-SIDED BREAST CANCER PATIENTS RECEIVING RADIOTHERAPY

A Research Project Report Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Medical Dosimetry

Lisa Wojtowicz

College of Science & Health Medical Dosimetry Program

July 2012

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July 23, 2012

BENEFITS, DISADVANTAGES, AND CHALLENGES OF RESPIRATORY GATING USED

TO TREAT LEFT-SIDED BREAST CANCER PATIENTS RECEIVING RADIOTHERAPY

By Lisa Wojtowicz

We recommend acceptance of this project report in partial fulfillment of the candidate's

requirements for the degree of Master of Science in Medical Dosimetry.

The candidate has met all of the project completion requirements.

Nishele Lenards, M.S. Date

Graduate Program Director

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The Graduate School University of Wisconsin-La Crosse

La Crosse, WI

Author: Wojtowicz, Lisa

Title: Benefits, disadvantages, and challenges of respiratory gating used to treat left-

sided breast cancer patients receiving radiotherapy.

Graduate Degree/ Major: MS Medical Dosimetry

Research Advisor: Nishele Lenards, M.S.

Month/Year: July 2012

Number of Pages: 50

Style Manual Used: AMA, 10th edition

Abstract

Left-sided breast cancer patients receiving radiation therapy may experience long term

effects to their heart resulting in cardiac toxicities. Respiratory gating is used in an effort to

decrease the radiation delivered to the cardiac tissues of these patients during treatment. This

research discusses the applicable scientific literature and specifically examines the use of

respiratory gating in a retrospective study. In this study, 10 left-sided breast cancer patients

treated with respiratory gating were analyzed for mean dose of radiation to the heart, left

ventricle, and lung volume. The dosimetric plan with respiratory gating was compared to the

non-respiratory gating scan. The results showed a 15.5% decrease in the mean dose delivered to

the heart and a 17.7% decrease in mean dose delivered to the left ventricle in the plans where

gating was used. A 15.4% increase in the lung volume being treated was also recorded. The

results of this research, which support the literature reviewed, affirm that respiratory gating is an

appropriate and effective method of limiting radiation exposure in left-sided breast cancer

patients receiving radiation therapy.

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The Graduate School University of Wisconsin - La Crosse

La Crosse, WI

Acknowledgments

Thank you to my director, Nishele Lenards and my mentor, Kim Schmidt for the

guidance and helpful advice throughout this research project. Many thanks to the entire radiation

oncology staff at Gundersen Lutheran Medical Center in La Crosse, WI. Thank you Lindsey

Shields, for taking the time out of your day to proofread and edit my research paper. Mom, thank

you for being my number one fan for the duration of the medical dosimetry program. Grandma

Mills you taught me that determination and perseverance are two of the most important skills in

succeeding in life goals. Dad, thank you for taking the time to listen and for helping me move

across states so I could take my first professional job as a medical dosimetrist. Thank you Jessie,

for your laughter and bright attitude could always bring a smile to my face. My dear family and

friends thank you so much for the words of encouragement along the way. I sincerely appreciate

all of the support and cheer during the exciting challenges I encountered in the medical

dosimetry program.

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Table of Contents

....................................................................................................................................................Page

Abstract ............................................................................................................................................3

List of Tables ...................................................................................................................................6

List of Figures ..................................................................................................................................7

Chapter I: Introduction.....................................................................................................................8

Statement of the Problem .................................................................................................11

Purpose of the Study.........................................................................................................12

Assumptions of the Study.................................................................................................12

Definition of Terms ..........................................................................................................12

Limitations of the Study ...................................................................................................17

Methodology ....................................................................................................................17

Chapter II: Literature Review ........................................................................................................19

Chapter III: Methodology ..............................................................................................................30

Sample Selection and Description....................................................................................30

Instrumentation.................................................................................................................30

Data Collection Procedures ..............................................................................................31

Data Analysis ...................................................................................................................31

Limitations........................................................................................................................31

Summary ..........................................................................................................................32

Chapter IV: Results........................................................................................................................33

Item Analysis....................................................................................................................33

Chapter V: Discussion ...................................................................................................................36

Limitations........................................................................................................................37

Conclusions ......................................................................................................................37

Recommendations ............................................................................................................38

References......................................................................................................................................48

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List of Tables

....................................................................................................................................................Page

Table 1: Percent volume of left lung receiving 20 Gy...................................................................39

Table 2: Average mean total lung (cGy) gating vs. non-gating scan.............................................39

Table 3: Average total lung volume (cm3) gating vs. non-gating scan..........................................39

Table 4: Average mean dose for the heart and left ventricle for the gating and non-gating

scans................................................................................................................................39

Table 5: Patient A gating scan treatment plan results....................................................................40

Table 6: Patient A non-gating scan treatment plan results ............................................................40

Table 7: Patient B gating scan treatment plan results ....................................................................40

Table 8: Patient B non-gating scan treatment plan results.............................................................40

Table 9: Patient C gating scan treatment plan results ....................................................................41

Table 10: Patient C non-gating scan treatment plan results...........................................................41

Table 11: Patient D gating scan treatment plan results..................................................................41

Table 12: Patient D non-gating scan treatment plan results ..........................................................41

Table 13: Patient E gating scan treatment plan results ..................................................................42

Table 14: Patient E non-gating scan treatment plan results...........................................................42

Table 15: Patient F gating scan treatment plan results ..................................................................42

Table 16: Patient F non-gating scan treatment plan results ...........................................................42

Table 17: Patient G gating scan treatment plan results..................................................................43

Table 18: Patient G non-gating scan treatment plan results ..........................................................43

Table 19: Patient H gating scan treatment plan results..................................................................43

Table 20: Patient H non-gating scan treatment plan results ..........................................................43

Table 21: Patient I gating scan treatment plan results ...................................................................44

Table 22: Patient I non-gating scan treatment plan results ............................................................44

Table 23: Patient J gating scan treatment plan results ...................................................................44

Table 24: Patient J non-gating scan treatment plan results............................................................44

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List of Figures

....................................................................................................................................................Page

Figure 1: Gating versus non-gating scans, percent volume of left lung receiving 20 Gy..............45

Figure 2: Average mean total lung dose (cGy) for the gating and non-gating scans measured ....45

Figure 3: Comparison of the gating and non-gating scan for the mean heart doses cGy ..............46

Figure 4: Comparison of the gating and non-gating scan for the left ventricle dose cGy .............46

Figure 5: Average mean dose for the heart and left ventricle for the gating and non-gating

scans................................................................................................................................47

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Chapter I: Introduction

Among women worldwide breast cancer is the most commonly diagnosed and deadliest

form of cancer.1 In the United States alone, 183,000 women are diagnosed each year with breast

cancer, of those women 40,000 die every year.2 Out of a group of nine women, in the United

States, one will develop breast cancer.2 Breast cancer rates vary widely by geographical area. The

lowest rates of breast cancer are seen in Asia and developing countries. Europe, Canada, and the

United States all have high incidences of breast cancer.3 Over the past several years the diagnosis

rate of breast cancer has fluctuated. During the 1980s, the number of patients diagnosed with

breast cancer grew due to improvements made in diagnostic exams.3 In 2003 the rate of breast

cancer diagnoses dramatically decreased due to research that showed a connection between

hormone replacement therapy for postmenopausal women and an increased chance for breast

cancer. After becoming aware of the effects of hormone replacement therapy women stopped

using the hormone replacement therapy.3

The likelihood of developing breast cancer is impacted by the following risk factors:

gender, age, family history, hormonal factors, past malignancy, previous benign breast disease,

diet and environmental factors, and radiation exposure.3 While men can also develop breast

cancer women have a much higher rate of developing breast cancer compared to men. The ratio

for men to develop breast cancer is 100 females to 1 male.3 Age is another important risk factor

noted in the development of breast cancer. As a woman ages, the chance that she will develop

breast cancer increases. The average age a woman develops breast cancer is 55 years old. The

majority of women that develop breast cancer are between the ages of 40 and 70 years old.3

Although diets high in fat have shown no connection to developing breast cancer, persons that

drink more alcohol are associated with an increased risk of breast cancer. Individuals who have

been exposed to radiation have an increased risk for developing breast cancer.3

Approximately 8 to 10% of breast cancer diagnoses are genetic.2 The genes breast cancer

susceptibility gene 1 (BRCA1) and breast cancer susceptibility gene 2 (BRCA2) are connected to

85% of breast cancer cases. The hormonal risk factors associated with breast cancer are related to

ovarian function, including early menarche, late menopause, and the removal of one or both

ovaries.3 A woman diagnosed with breast cancer in one breast has an increased risk for

developing breast cancer in the contralateral breast. When women have lobular carcinoma or

atypical hyperplasia in their breast their risk for developing breast cancer increases.3

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The “Edwin Smith Papyrus”, which documented medical events, is a historical record

written in 3000 to 2500 BC; in this time frame records indicate tumors of the breast existed but

there were no means for a cure.3 Over the past several years, countless research hours have been

devoted to determining the best form of treatment for breast cancer patients. Research from

Wang et al4 shows that breast cancer patients have an increased chance of survival after

undergoing one or a combination of the following: surgery, chemotherapy, and radiotherapy.

Whether or not these modalities are combined or used separately depend on the patient’s health

risks and needs.4 Radiation therapy has been proven as a vital form of treatment for breast cancer

patients to increase survival rates and decrease recurrence rates.4 Breast cancer patients

diagnosed with Stage 0, I, or II typically undergo surgery followed by radiation therapy.5 When

patients with early-stage and locally advanced disease undergo a lumpectomy followed by

radiation, local and regional recurrence rates significantly decrease, which increases patient

survival rate. This decrease in local regional recurrence after radiotherapy has been documented

over several studies; however, a patient’s survival rate is decreased due to radiation induced

cardiac morbidities. After a breast cancer patient receives radiotherapy, their chances of

developing heart disease later on in life increase.5

After a patient undergoes breast conserving surgery or radical mastectomy the patient

typically undergoes radiotherapy.6 The goal of radiotherapy after a patient undergoes a

mastectomy procedure is to decrease the rate of recurrence in the chest wall, skin, mastectomy

scar, and axillary, supraclavicular, and internal mammary nodes and to increase the overall

survival rate.7 The objective after a patient undergoes a lumpectomy is to deliver radiation to the

tumor region where microscopic disease may exist.7 The tangential beam arrangement was

designed to treat the breast tissue and nodal area when needed while decreasing the dose to the

normal structures (lung and heart) in the field.8 External radiation therapy for breast cancer is

typically delivered with lateral and medial tangential portals.6 Respiratory motion in the field is

also taken into consideration by increasing the anterior field border by 1-2 cm.8 The radiation

prescription is generally 45 Gy to 50 Gy, which is delivered to the breast tissue using tangential

fields.9 Although the heart dose in left-sided breast cancer patients has decreased in the past 40

years, the dose delivered to the heart can be over 20 Gy in some areas. Research has shown that

the heart receives an average mean dose of 2.3 Gy whereas the average mean dose of the left

anterior descending (LAD) coronary artery is 7.6 Gy.1 Radiation therapy in breast cancer patients

is also used as a form of adjuvant therapy to treat the margin around the lumpectomy cavity that

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may contain microscopic disease. Patients that receive breast-conserving surgery followed by

radiation therapy decrease the chance that cancer will develop again by a factor of 3 to 4.10

Studies have compared treatment modalities with and without radiation therapy. Research has

shown that patients have a 10% increase in survival over a 10-year span when treated with

systemic therapies (chemotherapy or hormonal therapy) in addition to radiation therapy.10

Patients may elect to receive partial breast irradiation which decreases treatment time and

may improve the patient’s quality of life.7 Partial breast irradiation is delivered through balloon

brachytherapy, interstitial catheter brachytherapy, and external-beam partial breast irradiation.

Patients selected for the partial breast irradiation therapy qualify for the procedure by having a

small risk for a tumor developing outside of the lumpectomy cavity. The patient’s age, histology,

tumor size, surgical margins, and nodal status are assessed to determine if the patient is at an

increased risk for failure outside of the lumpectomy cavity. The American Brachytherapy

Society and the American Society of Breast Surgeons have distributed strict recommendations

for patients considered for partial breast irradiation.7 The recommended dose fractionation

scheme for partial breast irradiation delivered by MammoSite is 3,400 cGy in 10 fractions. Two

fractions of 340 cGy are delivered twice per day. The MammoSite method places a balloon

inside the breast tumor volume volume. The balloon is linked to a catheter that is used to deliver

the high dose rate radiation.7

Although, radiation therapy has been documented to increase the survival rate amongst

breast cancer patients, left-sided breast cancer patients experience an increase in cardiovascular

mortality several years after receiving treatment. Research shows that 165 patients treated with

radiation for breast cancer between 1971-2001 resulted in a 44% higher rate of cardiac mortality

in left-sided breast cancer patients than those with right-sided breast cancer.1 Respiratory gating,

a technique used in radiotherapy breast cancer cases provides a means to decrease heart exposure

by adjusting treatments during respiratory motion.5 Respiratory motion incorporates the

diaphragm, heart, thoracic region, abdominal organs, and lungs. Inspiration is defined as

contraction of the diaphragm which results in an increase in thoracic volume while the

abdominal organs move downward. Expiration has the opposite effect; the diaphragm relaxes,

which causes a decrease in thoracic volume as the abdominal organs move upward.11 A four

dimensional computed tomography (4DCT) scan has the ability to capture the tumor and normal

structure movement during the respiration cycle.5 After the scan is complete clinicians analyze

the best phases of the patient’s breathing cycle where the tumor and the normal structures are

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separated the most. In the analysis of breast cancer patients, the amount of radiation delivered to

the heart is the primary area of concern. During respiratory gating procedures involving radiation

treatment of the heart, the point is to maximize the distance between the tumor and heart.5

Respiratory gating allows the treatment beam to coincide with the respiratory cycle of the

patient. The patient is treated at the optimal time during the patient’s breathing cycle in order to

decrease the radiation delivered to the heart.

Gating can be broken down into two categories, internal and external gating. Internal

gating uses a device implanted in the patient to track tumor motion. External gating uses an

external respiratory surrogate which is typically placed on the patient’s abdomen. There are two

types of respiratory gating: phase and amplitude gating. Phase gating is activated at a specific

width of the patient’s respiratory cycle, also known as the angular phase. The angular phase is

the specific phase of the breathing cycle the physician is interested in treating. Patients

undergoing radiotherapy with respiratory gating experience an extended treatment time because

the beam is only turned on at specific periods of their radiation treatment. Amplitude-based

gating demonstrates gating at the patient’s maximum inhalation phase. Amplitude gating is

activated at a specific vertical position of the breathing cycle, and is delivered at a time decided

upon by the physician. Patients receiving breast radiotherapy with amplitude respiratory gating

are treated on the patient’s inhale. During inhalation, the diaphragm draws the heart posteriorly

and inferiorly away from the chestwall, which reduces the amount of radiation delivered to the

organs at risk in the breast treatment field. The goal of respiratory gating when treating breast

cancer patients is to decrease the dose to the heart. In the patient’s inhalation phase, the heart has

the greatest separation from the target volume.12

Respiratory motion of the abdomen also plays a part in the dose homogeneity. Sidhu et

al13 examined three different types of treatment techniques and found that respiratory gating

increases the tumor coverage. Increasing the dose to the target volume and decreasing dose to the

normal structures is the foremost goal of dosimetry. Respiratory gating is a technique that

modifies treatment delivery to help achieve the primary goals set forth by the clinician to

increase the patient’s survival rate and decrease the chance for recurrence.13

Statement of the Problem

This retrospective research study evaluates radiation treatment for 10 left-sided breast

cancer patients. The patients chosen for the study were treated using respiratory gating at

Gundersen Lutheran Medical Center in La Crosse, WI during January through December of

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2011. This research was conducted to determine the amount of radiation delivered to the heart,

left ventricle, left lung, right lung, and total lung.

Purpose of the Study

This research study was developed to determine the benefits of the respiratory gating

procedure for left-sided breast cancer patients. The data collected and comparison analysis will

indicate the differences between the gating and non-gating scan treatment plans. A decrease to

the heart and left ventricle is expected in patients treated the respiratory gating procedure during

radiotherapy for breast cancer treatment. This research study is important to the quality of care

provided by radiation oncology staff to left-sided breast cancer patients. This study increases

awareness of treatment modalities and the outcome the treatment has on the patient’s longevity.

Assumptions of the Study

This study assumes that treating left-sided breast cancer patient with respiratory gating

will decrease the radiation dose delivered to the heart and left ventricle. The assumption that

respiratory gating will decrease the dose to the heart is based on research that shows that gating

increases the distance between the heart and target volume.

Definition of Terms

AP/LAT kV: The term AP/LAT kV refers to orthogonal reference images which are

used to review the accuracy of a patient’s setup position. AP stands for the image in the anterior

posterior plane and LAT for the lateral plane image. kV refers to kilovolts-peak which is peak

potential difference across the tube in units of 1000 volts. The linear accelerators produce kV

diagnostic x-ray images that are used to determine accurate patient setup.3

Active breathing control (ABC): The active breathing control method allows breathing

to be stopped at a specific phase of the respiratory cycle. The ABC method is used to help

physicians evaluate the patient’s respiratory cycle in relation to the tumor and normal structures

in the treatment area.7

Atypical hyperplasia: Atypical hyperplasia occurs when abnormal cells multiply in

normal tissue.3

Anterior myocardial territory (AMT): The anterior myocardial territory is defined

anatomically in the anterior region of the heart. The AMT receives a higher dose of radiation

during breast radiotherapy because it is adjacent to the chest wall and target volume.14

Balloon Brachytherapy: Balloon brachytherapy is a form of treatment for breast cancer.

Balloon brachytherapy is used for partial-breast irradiation therapy. The balloon brachytherapy

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procedures use a single source of radiation, which is placed in the center of the balloon that is

inserted into the patient’s lumpectomy cavity.15

BBs: BBs are small metal balls placed on the patient. The BBs are visible on the CT

images. The BBs are used to define the setup and/or treatment area for a patient.3

Beamlet intensity modulated radiation therapy (Beamlet IMRT): Beamlet intensity

modulated radiation therapy is a radiation treatment method used to increase the dose conformity

of breast cancer dosimetric treatment plans. Beamlet IMRT gives radiation in small subfield

intensity patterns.8

Breast cancer susceptibility gene 1 (BRCA1): BRCA1 is a human gene tumor

suppressor. In typical cells BRCA1 maintain the healthy cell’s genetic information and stop

proliferation of atypical cells. When BRCA1 mutates a relationship is seen between the mutation

of the BRCA1 tumor suppressor gene and breast cancer.16

Breast cancer susceptibility gene 2 (BRCA2): BRCA2 is a human gene tumor

suppressor. In typical cells BRCA2 maintain the healthy cell’s genetic information and stop

proliferation of atypical cells. When BRCA2 mutates a relationship is seen between the mutation

of the BRCA2 tumor suppressor gene and breast cancer.16

Breast conserving surgery: Breast conserving surgery is a surgical procedure that

removes only the tumor from the breast.7

Centigray (cGy): Centigray is a unit of that indicates the amount of energy absorbed per

unit mass of any substance. cGy is used to measure radiation absorbed into material. One unit of

Gray is equivalent to 100 cGy.3

Clinical target volume (CTV): The clinical target volume is defined as the tumor seen

on diagnostic imaging scans and/or is palpable on physical exam. The clinical target volume also

includes a margin that takes into account microscopic tumor that should be part of the treatment

volume.3

Computed tomography (CT): Computed tomography is a three-dimensional (3D)

image that shows spatial location of skin, tumor, normal organs and tissues. The 3D image is a

reconstruction of the patient’s physical anatomy and electron density. The electron density is

used to account for inhomogenity corrections.17 CT scans are used in radiation oncology to

create the dosimetric treatment plan.

Conformity Index (CI): The conformity index is a tool used to quantify how a radiation

treatment plan conforms to the target volume in terms of dose distribution.18

14

Conventional wedged technique (CWT): Conventional wedged technique is a method

used to treat breast cancer patients with radiation. The CWT uses a tangential field arrangement

to treat the breast volume and nodes if needed while decreasing the dose to the normal structures.

Wedges are used in the conventional technique to increase the dose distribution to the breast

tissue.8

Coverage Index: The coverage index is used to describe the fraction of the target that

receives a dose equal to or greater than the target dose.7

Deep-inspiration breath hold (DIBH): During the deep-inspiration breath hold method

a patient is instructed to take a deep inspiration and hold their breath for the duration of the

radiation treatment. This technique may increase the distance between the heart and chest wall.4

Digitally reconstructed radiographs (DRRs): DRRs are created from CT images. The

DRRs display the beam’s eye view of the treatment field, which is a calculated projection of an

x-ray image. The DRR is used to view patient anatomy.3

Distance from left ascending aorta (DLAA): The distance from the left ascending aorta

is a physical measurement that indicates the distance from the left ascending aorta to a marked

line (between the middle point of the sternum and the body) on each CT slice.5

Electronic Portal Imaging Device (EPID): The electronic portal imaging device

delivers near real-time portal images. The EPID is located on the linear accelerator and is used to

aid in accurate patient setup.3

End of expiration (EE): Expiration takes place when the diaphragm relaxes which

decreases the thoracic volume while the abdominal organs move up. The end of expiration

occurs when the diaphragm is relaxed.11

End of inspiration (EI): Inspiration is defined as the contraction of the diaphragm which

results in an increase in thoracic volume. During the contraction of the diaphragm the thoracic

volume increases. The end of inspiration is the end of the contraction of the diaphragm.11

Fiducial markers: Fiducial markers are either artificial implants, surface markers, or

patient anatomy that help define anatomical location internally or on the patient’s surface.3

Four dimensional computed tomography (4DCT): 4DCT combines three dimensional

treatment planning and time.3

Free breathing (FB): During a free breathing scan patients are instructed to breath

normally and quietly.8

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Gray (Gy): Gray is an international standard unit that quantifies the absorbed dose. The

Gy is used to measure radiation absorbed into material. One unit of Gray is equivalent to 100

cGy. 3

Homogeneity Index: The homogeneity index is used to quantify the dose uniformity in

the target volume.7

Inhomogenity corrections: Inhomogenity corrections account for the difference in tissue

density in treatment plans.3

Inspiration gating (IG): Inspiration gating is a method used in breast radiotherapy

treatments that delivers the radiation during the inspiration period of the respiratory cycle.19

Intensity modulated radiation therapy (IMRT): - Intensity modulated radiation

therapy is used to deliver nonuniform radiation with different methods and treatment machines

across the beam’s eye view.3

Interstitial catheter brachytherapy: Interstitial catheter brachytherapy is used for

partial breast irradiation treatment. Interstitial catheter brachytherapy uses catheters to implant

small radiation sources in the tissue for irradiation.7

Ischemic heart disease: Ischemic heart disease occurs when patients are unable to pump

an adequate amount of blood to the body. Ischemic heart disease develops when the blood

vessels used to deliver blood and oxygen become too small.20

Left anterior descending (LAD) coronary artery: The left anterior descending artery is

anatomically located near the major coronary vessel in breast radiation treatment fields. The

LAD coronary artery may be used as an organ at risk during breast radiotherapy.21

Lobular carcinoma: Lobular carcinoma occurs when cancer develops in the glands that

produced milk (lobules).23

Lumpectomy: A lumpectomy is a procedure a patient undergoes to remove disease in

the breast and a margin around the disease. A lumpectomy is a form of breast conserving

surgery.3

MammoSite: The MammoSite applicator is used for breast brachytherapy. The

MammoSite applicator is used to implant radiation to the breast tissue surrounding the

lumpectomy cavity. The MammoSite applicator is a double-lumen catheter with a balloon. The

balloon is enlarged after the catheter is inserted into the lumpectomy cavity.15

Maximum heart depth (MHD): The maximum heart depth is defined by the distance

from the front of the heart to a line that connects the middle point of the sternum and body.5

16

Normal tissue complication probability (NTCP): The NTCP is used to determine the

potential of a complication in terms of dose and volume.7

Partial Breast Irradiation: Partial breast irradiation is a form of breast cancer treatment

that delivers a high dose of radiation in a shorter period of time to the region of the breast where

disease was present.15

Planning target volume (PTV): The planning target volume includes the clinical target

volume (CTV) with an additional margin. The margin added to the CTV increases the treatment

volume to account for patient setup and patient motion.3

Real time position management (RPM) System: The real time position management

system is used during radiation therapy treatments to track respiratory motion of the patient. By

tracking the patient’s breathing cycle the system is able to turn the radiation beam on and off

based off of the patient’s respiratory rate. The RPM system is used to treat patients that have

disease in the lungs, liver, pancreas, and heart.12

Real-time tumor tracking (RTTT) system: The real-time tumor tracking system

includes four sets of diagnostic x-ray images. The RTTT system includes an image processor

unit, gating control unit, and image display unit. Two of the systems provide a clear view of the

patient at all times. The RTTT system uses a 2 millimeter (mm) gold marker implanted in the

patient to track the position of the tumor 30 times per second. The linear accelerator delivers

radiation when the gold marker is within a specified tolerance based off of the patient’s

respiratory cycle.22

Respiratory Gating: Respiratory gating is used in radiotherapy to account for breathing

movement. To compensate for the movement of target volumes and normal structures during the

patient’s respiratory cycle, respiratory gating is used to turn the beam on and off when

appropriate during treatment. A device is placed on the patient’s abdomen and is monitored

during the patient’s treatment to track the breathing cycle.7

Segment intensity-modulated radiation therapy (SIMRT): Segment intensity

modulated radiation therapy is a radiation treatment method used to increase dose uniformity and

decrease the amount of radiation delivered to the normal structures. SIMRT uses a bigger

radiation field to deliver multiple field segments.8

Target Volume: The target volume is the region where tumor is known to be present or

suspected.3

17

Three dimensional (3D) conformal radiotherapy (3DCRT): 3DCRT uses 3D imaging

and treatment planning computers to design a radiation treatment that conforms the radiation

dose to the treatment volume while decreasing the radiation being delivered to normal

structures.3

Two dimensional array of ion chambers: Ion chamber is a device that measures

ionizing radiation by collecting the charge of electrodes. 24

Voluntary deep inhalation breath hold (VDIBH): The voluntary inhalation deep breath

hold method is used when treating breast cancer patients. The method reduces the radiation

exposure to the heart during left-sided breast cancer patient treatments without losing target

coverage. The patient voluntary holds their breath during the radiation treatment.25

Limitations of the Study

Ten left-sided breast cancer patients were randomly selected for this retrospective

research study that analyzed the effects of respiratory gating. The small sample size used in this

retrospective study gives limited research data. An increase in sample size would have given

more patient data and allowed for more accurate data analysis. The original treatment plan based

off of the respiratory gating scan was transferred to the non-respiratory gating scan. The patient

remained in the same supine setup as the gating scan; however, there might have been slight

movement in the patient’s position between scans. After the plan was transferred to the non-

gating scan the isocenter was verified by orthogonal DRRs for accuracy. Confirming the

placement of isocenter is done manually, which may result in slight human error. The structures

measured in the study consisted of the heart, left ventricle, left lung, right lung, and total lung.

These patient contours were performed by physicians, medical physicists, and medical

dosimetrists. Since the patients were contoured by different members of the radiation oncology

team there may be slight variations in the volumes studied. Patients selected for the study did not

receive intravenous contrast to highlight the left ventricle structure. Without intravenous contrast

the left ventricle was more difficult to contour.

Methodology

Ten patients treated for left-sided breast cancer with respiratory gating at Gundersen

Lutheran Medical Center in La Crosse, WI during January 2011-December 2011. The 10 patients

were selected at random for this retrospective research study. This study analyzed left-sided

breast cancer patients treated using respiratory gating compared to patients treated without

respiratory gating. To compare the 2 dosimetric plans developed on the gating and non-gating

18

scans contours were created for the heart, left ventricle, right lung, left lung, and total lung on

each scan. The treatment plan developed on the respiratory gating scan was transferred to the

non-respiratory gating scan and verified using orthogonal DRRs to verify the treatment isocenter.

The treatment plan was re-calculated and the dose was recorded for the heart, left ventricle, left

lung, right lung and total lung. The two plans were reviewed to determine the role respiratory

gating played in decreasing the amount of radiation delivered to the heart.

19

Chapter II: Literature Review

Breast cancer has the highest rate of diagnosis and fatality among women worldwide.1

The rate of breast cancer varies by patient location. The highest rate of breast cancer is seen in

Europe, Canada, and the United States.3 Risk factors for breast cancer are gender, age, genetics,

hormonal factors, previous cancerous and/or benign tumor, diet, environmental factors, and

previous radiation exposure.3 Patients with breast cancer are treated with surgery, chemotherapy,

and radiotherapy alone or are combined for therapeutic treatment.4 The radiation techniques used

to treat breast cancer include a tangential beam arrangement with a dose prescription of 45 Gy.

Left-sided breast cancer patients have a higher rate of developing cardiac mortality.1 A patient’s

breathing cycle creates movement in the treatment field to account for this movement respiratory

gating is used to increase the distance between the heart and target volume.5 Patients with breast

cancer have seen a decrease in recurrence after receiving breast radiotherapy.5 However, after

being treated with breast radiotherapy patients have exhibited an increase in cardiac morbidities

along with heart disease later in life.5 This literature review consists of research about left-sided

breast cancer patients that receive radiation therapy with the addition of respiratory gating.

Various methods of radiotherapy that incorporate respiratory gating were reviewed along with

when it is appropriate to use respiratory gating in a patient’s treatment. Technological advances

require monitoring, which is why accurate quality assurance of respiratory gating is necessary to

provide safe and effective treatment to cancer patients. Thus the challenges of quality assurance

for respiratory gating procedures will also be reviewed.

Breast cancer patients may develop cardiac disease due to radiation exposure even if

cured of the cancer. Although there is a relationship between breast cancer radiotherapy followed

by cardiac disease the connection between specific cardiac volumes and heart disease has not

been clearly documented. Many retrospective studies have been documented that show a

connection between radiation therapy to the breast and heart disease.21 Feng et al21 note that the

LAD coronary artery is near the major coronary vessel in the breast fields which is why

monitoring the dose to the LAD coronary artery during breast radiotherapy is relevant. Radiation

exposure to the pericardium, myocardium, valves, conduction system, and autonomic system

have also been studied and found to have detrimental effects after radiotherapy.21 In order to

develop a consistent approach to contouring the heart and substructures Feng et al21 collaborated

with physicians. The atlas was developed through the combinational efforts of a cardiologist, a

cardiac radiologist, and a radiation oncologist. The computed tomography CT images used in the

20

creation of the atlas were done with respiratory gating and with and without intravenous contrast.

After the contours were defined by the team of physicians, they were used as a key for a group of

radiation oncologists used in the atlas validation process.21 To determine if the atlas was a valid

tool for contouring, radiation oncologists contoured structures of the heart and substructures

prior to reviewing the atlas and after reviewing the atlas. After reviewing the atlas the accuracy

of the structure contours increased which is how the atlas was validated.21 Patients were

simulated in the supine position utilizing a breast board with their arms placed overhead.

Physicians contoured the heart, left main artery, LAD coronary artery, interventricular branch,

left ventricle, and right coronary artery prior to seeing the atlas and after consulting the atlas.

Feng et al21 acknowledged that the atlas limitations were due to sample size and the use of

respiratory gating. However, Feng et al21 believed that the atlas would help create a more

standardized approach to contouring the heart and substructures. Thus, the atlas will increase the

accuracy and records of exposure for breast cancer patients being monitored.21

Tan et al14 have studied the anterior myocardial territory (AMT) in comparison to the

heart as an organ at risk (OR) for breast radiotherapy. Researchers created 5 breast IMRT plans

to analyze the heart, left ventricle (LV), AMT, LV and AMT, and the heart and LV.14 All 23

patients studied had left-sided breast cancer and were simulated in the supine position. The level

of priority was assigned in the following order, highest first: PTV (defined by specific margins),

heart, LV and AMT, lungs, and the right breast.14 The Tan et al14 study measured the

homogeneity index, conformity index, and coverage index for five IMRT plans for each patient.

The five IMRT plans consisted of heart (H), left ventricle (LV), AMT, LV + AMT, and H + LV

as the primary constraints. The results showed that the IMRT – AMT, IMRT – LV and IMRT –

LV + AMT IMRT plans did not compromise the homogeneity index, conformity index, and

coverage index but were able to reduce the mean dose to the heart, LV, and AMT when

compared to the IMRT – H plan. The IMRT – AMT plan and the IMRT – H + LV were

compared and demonstrated minimal differences that were not clinically significant.14

Data has shown the link between radiation therapy to the chest and heart disease.14 The

Tan et al14 study is important because radiation is not the only form of treatment for breast

cancer that has negative effects on the heart. In addition to radiation therapy the drug

combination of Anthracycline and Trastuzumab may also affect the heart and cause heart disease

further on in the patient’s lifespan.14 Anthracyclines is a medication used in breast cancer

chemotherapy. Trastuzumab is a monoclonal antibody used in combination with chemotherapy

21

to treat breast cancer.14 Patients who receive chemotherapy and radiation therapy have an

increased risk for developing cardiac problems because of the chemotherapy medications. The

side effects of radiotherapy treatments can be categorized either as acute or chronic. The acute

reaction is normally pericarditis; chronic developments are pericardial disease and coronary

artery disease, which can develop years after left-sided breast cancer radiation treatment.5 The

long-term effects of the cardiovascular disease consist of pericarditis, ischemic heart disease, and

myocardial infarction, and may be fatal in some cases. After scientific investigation, two

prominent developments have been noted. First, after a patient undergoes treatment for breast

cancer that includes radiation fields of the breast tissue or chest wall, the heart tissue is damaged

from radiation. Due to the anatomical location of the heart in relationship to the target volume of

treatment, the heart tissue is compromised. Secondly, long-term survivors of breast cancer have

an increased risk of cardiac induced fatalities. Left breast cancer patients are at an increased risk

due to the tumor volume and coinciding treatment fields.5

Breast cancer patients receiving radiotherapy for treatment of their disease increase their

chance of survival; however, patients also increase their chance of developing heart disease from

radiation to the heart. Patients with left-sided breast cancer have an increased risk because the

heart is exposed to a greater amount of radiation. A typical planning method for breast cancer

radiation includes a three-dimensional conformal radiotherapy (3DCRT) plan. The 3DCRT

consists of two tangential beams with the addition of wedges. This beam arrangement has been

shown to decrease the amount of radiation delivered to the heart.5 A three-dimensional CT

(3DCT) is typically used for the image data set for treatment planning. However, a 3DCT does

not have the capability of capturing images in motion thus the treatment area is not as accurate

because it does not represent the movement of the tumor and normal structures during the

respiratory cycle.5 The advent of 4DCT planning and respiratory gating has improved the quality

of care for patients with tumors that are affected by respiratory motion. 4DCT allows the

clinicians to view the image data set in different phases of the respiratory cycle so the tumor and

the nearby structures may be seen more clearly, which will help indicate when respiratory gating

should be used.5 The study performed by Qi et al5 used 4DCT images to examine the maximum

heart depth (MHD) and the distance from the left ascending aorta (DLAA) to determine if they

are markers that can be used at simulation to determine if respiratory gating should be used in

treatment. The researchers found that both MHD and DLAA markers can be used either in

combination or independently to determine if the patient should receive respiratory gating.5

22

Innovative radiotherapy treatment techniques have been developed by researchers for

breast cancer patients. Cao et al8 compared three different treatment planning techniques,

conventional wedged technique (CWT), segment intensity-modulated radiation therapy

(SIMRT), and beamlet IMRT (IMRT) to determine target coverage and dose to the normal

structures in relationship to respiratory motion. CWT method has been the technique of choice

for treating breast cancer in the past; however, patients that have larger breasts have an increase

in dose to the lung and heart while the breast tissue dose coverage is inhomogeneous.8 In order to

create a more optimal treatment plan, SIMRT or IMRT techniques are used to decrease the

amount of hot spots while delivering less dose to the normal structures. This study featured an

active breathing control (ABC) procedure.8 Active breathing control is a method that measures

breathing cycles and stops breathing at a specific phase of the respiratory cycle.7 Overall there

was not a significant change to the clinical target volume (CTV) in respect to respiratory motion

when using the planning techniques CWT and SIMRT. Although the IMRT plans were

conformal, respiratory motion modified target dose coverage. There were significant changes in

target coverage for the IMRT plans which led the researchers to recommend that respiratory

motion be accessed when the patient is simulated for treatment. If the medial marker motion is

less than 0.6 cm, a predetermined value, which can be measured from an end of expiration (EE)

and end of inspiration (EI) CT simulation scan or 4DCT, then the IMRT treatment modality is

appropriate for use. However, if the medial marker motion is greater than 0.6 cm respiratory

gating is needed to achieve adequate tumor coverage and limit the dose to the lungs and heart.8

A study performed by Borger et al26 examined the exposure to the heart when comparing

left and right-sided breast cancer. This is an important study to consider in terms of the use of

respiratory gating. This study concluded that left-sided breast cancer patients have an increased

risk for developing cardiovascular disease.26 This study included 1601 patients treated for breast

cancer during 1980 and 1993. Out of the 1601 patients 94% were compliant in follow-up. The

patients were treated using tangential beams at five different hospitals. Cardiovascular disease

was seen in 14.1%, ischemic heart disease 7.3%, and other forms of heart disease, 9.2%. Patients

started experiencing heart disease 10 to 11 years after radiation therapy. Patients who received

left-sided breast cancer radiotherapy had a greater incidence of cardiovascular disease (16%)

compared to those who had right-sided radiation (11.6%). This study measured the maximum

heart depth (MHD) to determine if the risk for developing cardiovascular disease increases when

23

larger irradiated heart volumes are used in treatment. The study concluded that there was no

clinical significant increase in patients treated with larger heart volumes.26

Patients being treated for breast cancer by means of radiotherapy have been shown to

develop ischemic heart disease which may lead to death. After several studies reported the

elevated dose to the heart, numerous procedures were examined to decrease the heart dose.

Respiratory motion and intensity modulated planning were used to decrease the dose. A recent

study by Wang et al4 found it is important to monitor the patient’s cardiac motion, independently

of the patient’s respiratory cycle during deep-inspiration breath hold (DIBH). The researchers

looked at how much radiation was delivered during treatment of the breast to the posterior and

LAD coronary artery. Upon conclusion of the study, the researchers recommended that the LAD

coronary artery remain at least 5 mm from the field edge to decrease exposure to the heart.4

Left-sided breast cancer patients have been shown to experience more cardiac toxicity

after radiation therapy. Correa et al27 conducted a study to review the relationship that existed

between radiotherapy, cardiac markers, and clinical diagnosis of cardiac disease. The study

found a higher number of patients treated for left-sided breast cancer by the conventional

tangential beam method were experiencing latent heart tissue toxicities which were documented

by patient symptoms and abnormal laboratory values. The region of the heart damaged by the

radiation breast field was the LAD coronary artery. The research study stated 3DCRT, which is

currently the standard way of treating breast cancer patients, dramatically decreased dose to heart

and improved the survival rates of breast cancer patients.27

The heart is a known concern to radiation oncologists when prescribing radiation to the

breast region. The patient’s lungs are another normal structure included in the radiation field and

require additional attention to decrease the chances of the patient developing pneumonitis.

Korreman et al28 performed a retrospective study that included 33 patients. All of the patients in

the study had DIBH and free breathing (FB) scans, 17 of the patients had an inspiration gating

(IG) scan. The study evaluated cardiac damage and pneumonitis in patients receiving

radiotherapy after surgery. Researchers used radiobiological normal tissue complication

probability (NTCP) models to examine the probability of cardiac and pneumonitis complications.

This research showed a decrease in pneumonitis and cardiac mortalities after evaluating the

NTCP calculated values for patients treated with breast radiotherapy. The results demonstrated

that DIBH and IG make a significant impact on decreasing the patient’s chance of dying from

cardiac issues created by radiation and decreasing the likelihood of developing pneumonitis.28

24

The radiation treatment plan has evolved over several years to create an optimal plan that

covers the breast tissue accurately while decreasing the dose to the normal structures. McIntosh

et al 25 reviewed the reproducibility of patient setups for left-sided breast cancer patients during

deep inhalation breath hold treatments. Women treated for left-sided breast cancer were

documented as having increased cardiac symptoms. The symptoms included chest pain, coronary

artery disease, and myocardial infarction. Stress tests were done amongst right-sided and left-

sided breast cancer patients. The results from the stress tests showed abnormal results in 70% in

the patient’s LAD coronary artery of the left-sided breast cancer patients receiving radiation

therapy. The McIntosh et al 25 study used the Varian real-time position management (RPM)

system to examine the voluntary deep inhalation breath hold (VDIBH) method rather than the

ABC. The VDIBH and ABC method are used to decrease the radiation exposure to the heart

while maintaining the physician designated tumor volume. The LAD coronary artery and heart

radiation exposure is decreased when using the VDIBH because it increases the amount of space

between the breast target and heart. This study, which included 10 patients, examined the ability

to position a patient in the same position in the treatment appointment as was used in the

simulation appointment.25 This study was the first to examine VDIBH in the heart location in

three dimensions during treatment.25 In order to determine the patient setup accuracy for the

patient’s treatment the researchers co-registered orthogonal AP/LAT kV images. By measuring

these images the researchers were able to determine the relationship between the displacement of

the external RPM marker motion and the internal bony anatomy breath hold.25 Since the heart

dose was determined the heart volume used was shifted in alignment with the bony anatomy. The

researchers report that the shifts were minimal so they did not take into effect heterogeneity

differences in tissue.25

The McIntosh et al 25 study determined, that the VDIBH technique offered three positive

functions.

1)The heart moves inferiorly and posteriorly with respect to the left breast, distancing the

heart from the left anterior chest wall; 2) breath hold immobilizes the whole breast and

lumpectomy cavity, reducing PTV expansions for respiratory motion; and 3) it is relatively

inexpensive and can be widely adopted in most clinics.25

The radiation delivered to the heart was drastically reduced using the VDIBH technique. The

median heart dose volume getting more than 50% of the prescribed radiation dose went from

19.2% (FB technique) to 1.9% (VDIBH technique) The median LAD coronary artery volume

25

receiving more than 50% of the prescription dose went from 88.9% (FB technique) to 3.6%

(VDIBH technique).25 The overall difference in the ability to reproduce the patient setup during

treatment was a maximum of 3 millimeters. Through the research conducted, the team was able

to develop a standardized VDIBH radiation therapy procedure for left-sided breast cancer

patients. The standard procedure enabled the group to determine the amount of radiation

exposure to the heart and LAD coronary artery when using the VDIBH technique. The

evaluation of the results concluded that the VDIBH technique decreases the heart dose compared

to the FB technique and is an effective form of treatment because of the reproducibility level.25

In a study similar to McIntosh et al,25 Borst et al 29 evaluated the effect of image-guided

deep inspiration breath hold during breast radiotherapy. Borst et al29 examined 19 patients treated

with the deep inspiration breath hold (DIBH) procedure. Researchers determined the dose

delivered to the ipsilateral breast/thoracic wall, heart, (LV), and the LAD coronary artery. The

DIBH technique was compared to the FB technique. The reproducibility for the technique was

also measured during treatment. The patient position was modified during setup with the use of

cone-beam CT (CBCT) and observed by the 2D fluoroscopy and megavoltage electronic portal

imaging device (EPID) images.29 The Borst et al29 study demonstrated that the DIBH procedure

was simple to implement for treatment and decreased the dose to the heart, LV, and LAD

coronary artery without compromising the dose delivered to the target volume. Borst et al29

acknowledged limitations to the study, such as contrast not being used which impacted the LAD

coronary artery structure definition. Researchers contoured the first part of the LAD coronary

artery which was visible on all patients to develop consistency. The setup error was determined

for the breast and the organs at risk. Researchers found that the setup error did not have clinical

implications on the target volume and organs at risk.29

As the treatment modalities have improved over the years the longevity of breast cancer

patients has also increased. In order to decrease the cardiac toxicities associated with radiation

therapy in left-sided breast cancer patients, the dose to the heart needs to decrease to spare the

heart tissue. In addition to the radiation dose to the heart, the heart is also at an increased risk for

damage from the advanced, but severe cardiotoxic agents used in chemotherapy. There are

numerous studies that discuss how respiratory motion affects the dosimetric data treatment plans

and include the evaluation of respiratory motion and dose to target and avoidance structures in

terms of respiratory gating procedures.

26

Orlanzino et al30 selected 12 patients to evaluate the need for respiratory gating in

patients being treated for breast cancer with radiation therapy. Researchers were interested in the

relationship between the breast volume and chest wall interface since the target moves during

respiratory motion. The study was conducted to determine if the respiratory gating procedure

was necessary in radiation treatment of breast cancer. The study used a Varian Acuity simulator

to measure the movement between patient’s intact breast and chest wall. The distances between

the 2 volumes were measured using orthogonal anterior and lateral images. All 12 patients were

simulated in the supine position and utilized typical immobilization techniques for breast

patients. To quantify the distance between the breast target volume and chest wall during scans

BBs were placed at isocenter, and at 5 cm superior, inferior, lateral, and medial.30 The study was

interested in determining the patient’s normal respiratory pattern so patients were not given

guidelines for breathing during the scans.30 A typical breathing rate is 16-18 breaths per minute,

so the researchers obtained the images in 20 second intervals to measure the breathing pattern of

patients for 5-6 breathing cycles. The images were obtained for every one second period. The

results showed minimal movement between the target breast volume and chest wall. The average

maximum distance between the target breast volume and chest wall BBs were: 1.83 mm ± 1.08

mm sup-inf, 0.58 mm ± 0.21 mm lat-med, and 1.90 mm ± 1.04 mm ant-post axes.30 The study

concluded that the respiratory gating procedure used in breast cancer radiotherapy would not

have a large impact on the target volume in the efficacy of treatment. Researchers proposed that

improving image-guided localization as opposed to target motion may be more important in

improving the breast cancer radiotherapy.30

Aznar et al24 also studied breast cancer treatment in terms of efficacy of radiation therapy

similar to Orlanzino et al.30 The team of researchers was interested in the various respiration

patterns and the gating window range when using amplitude-gating when delivering radiation by

3DCRT and IMRT treatment plans. The study used the Varian Medical systems RPM method

and two-dimensional (2D)-array of ion chambers.24 The researchers devised specific methods to

evaluate the respiratory gating procedure.24 The breathing rate was quantified for two respiratory

cycle intervals, which were 4 and 6 seconds along with 5, 10, and 25 mm degrees in motion. The

gating window settings used were, 1.5, 2.4, and 5 mm. Researchers concluded that the

respiratory gating procedure improved the radiation delivery outcome.24 Aznar et al24

demonstrated that respiratory gating also improves the treatment delivery to the tumor volume

through the use of respiratory gating. Researchers used the gamma index (3%, 3 mm, dose range,

27

5-500% and 90-500%) in combination with determining the variance among the hot and cold

spots in the treatment plan.24 After analyzing the results, Aznar et al24 concluded that respiratory

gating gave a gamma pass rate and did not have hot and cold spots in the dosimetric plan from

the patient’s respiratory motion. The efficacy tumor volume results obtained by Aznar et al24

study contradicted the results found by Orlanzino et al.30

Accurate quality assurance (QA) is needed in all aspects of radiation therapy. QA for

respiratory gating has unique challenges because of the added temporal dimension.31 The goal of

the QA is to ensure clinically accurate treatment is delivered when respiratory gating is used.31

One main issue for respiratory gating and breath holding QA is determining treatment accuracy

when the internal target is indicated using external replacements. Testing of the software and

hardware is needed to ensure proper simulation, planning, patient localization, treatment, and

verification.31 Respiratory gating can be broken down into two different methods: internal and

external. The more common form of gating is external gating. In an external gating system the

box is placed on the patient’s abdomen. Fiducial markers are an example of an internal gating

system.31 Internal gating systems are not used often because they are only used in the real-time

tumor tracking (RTTT) system. An inaccuracy foreseen in respiratory gating is the determination

of tumor location from external breathing signals. Over time, the relationship between tumor

movement and the box signal change interfractionally and intrafractionally.31

In an effort to examine QA techniques for respiratory gating, Jiang et al31 used RPM by

Varian; this system uses the motion created by the abdomen as the signal. The following QA

procedure is recommended by Jiang et al.31 1.During treatment simulation, the reference home position should be accurately measured, using

techniques such as 4D CT. 2. During treatment planning, the patient and tumor geometry corresponding to

the gating window should be used. 3. During patient setup, the tumor home position at this fraction should

be matched to the reference home position. 4. During the treatment delivery, measures should be taken to

maintain a constant tumor home position, i.e. the tumor should always be at the same position when the

beam is turned on. 5. During the treatment delivery, tumor positions corresponding to the gating window

should be measured and compared with the reference tumor home position, either on- or offline.31

Jiang et al31 stated that steps one and two are simple while step three requires more effort and

they advise that image guidance techniques be used to ensure that the tumor home position and

the reference home position match. This is an important step because it will help decrease the

inter-fraction difference amid the external surrogate signal and the internal target location. Step

four states that the tumor should always be at the correct position when the beam is turned on. To

28

increase the accuracy, patient breath coaching is used. Massachusetts General Hospital

developed a system that requires a patient to wear video goggles in order to view their own

breathing pattern. The patient watches the video and aims to put their end of exhale position

between two lines; this additional QA step is necessary at simulation, patient setup, and

treatment delivery to ensure consistency. Step five is needed to monitor that the tumor location is

within the gating window. During treatment, the patient is monitored by watching the location of

the tumor in comparison to the reference position and tolerance zone. If the patient’s tumor

location does not lie within the tolerance zone, the therapist is able to stop treatment and adjust

the patient.

The treatment for left-sided breast cancer patients has been continuously evaluated in

order to decrease the dose to the heart which in turn would decrease the patient’s probability of

developing cardiac toxicities. Borer et al26 completed a retrospective study for left and right-

sided breast cancer patients to determine if there was an increased risk for patients treated on the

left-side. Researchers found that left-sided cancer patients were more likely to develop cardiac

problems later on.26 To track the dose to the heart and substructures, Feng et al21 developed an

atlas to help define these structures. Defining the OR with accurate consistency is an important

factor in measuring the normal structures in the field along with deciding the optimal OR for

treatment sites. Previous studies have documented the heart as an OR. Tan et al14 studied the

AMT in comparison to the heart in breast radiation therapy. The Tan et al14 study concluded that

when using the AMT as an OR the treatment plan did not compromise dose coverage while

decreasing dose to the heart. The patient’s lungs are also a concern during treatment. Korreman

et al28 determined that patients utilizing DIBH and IG during breast radiotherapy treatment

significantly decreased the chance of developing cardiac problems later on and lessening the

chance of developing pneumonitis. The combination of breast radiotherapy and chemotherapy

have shown to increase the probability that a patient will develop cardiac problems.14 The

anatomical location of the breast tumor and heart changes during the patient’s breathing cycle. It

is necessary to account for the physical displacement between the tumor and the heart in order to

increase the efficacy of the treatment and decrease the radiation exposure to the heart. To

decrease the dose to the heart 3DCRT has been used as a form of treatment planning to decrease

the amount of radiation delivered to the heart. Three dimensional computed tomography images

are used to develop radiation treatment plans. However, 3DCT is unable to capture the

movement of the tumor and normal structures in the radiation field. Qi et al5 used 4DCT images

29

to examine the MHD and DLAA to decide if respiratory gating would be suitable for treatment.

Cao et al8 studied SIMRT, beamlet IMRT, and CWT to decide how respiratory motion effected

target coverage in these treatment techniques. The study concluded that respiratory motion did

not significantly affect tumor coverage for the plans using the CWT and SIMRT. However,

significant changes were seen in the IMRT tumor coverage because of respiratory motion. The

treatment modalities have improved over the years for left-sided breast cancer patients. During

this development QA techniques have also been addressed for respiratory gating to ensure that

the treatment delivered is accurate. Jiang et al31 gave guidelines to follow during the patient

simulation and treatment process.

Several studies have researched breast cancer radiotherapy techniques and methods for

measurement to define and provide optimal treatment. Breast cancer patients are at an increased

risk for developing cardiovascular disease. Respiratory gating is used to decrease the dose to the

heart during left-sided breast cancer treatment. Accurate contours will help monitor the radiation

dose delivered to organs at risk in the field. The standard OR in left-sided breast cancer patients

have been the heart and lung volumes. To further decrease the damage done to the heart by

radiation researchers have investigated other OR. The AMT and LV have been documented as

pertinent OR during treatment plan optimization rather than the heart alone. Researching other

organs at risk provides direct links to the cause behind cardiovascular disease in left-sided breast

cancer patients. Researchers determined that patients treated using respiratory gating did not

have hot and cold spots that may normally be there from tumor respiratory movement. Quality

assurance is difficult for respiratory gating because of the added temporal dimension. Therefore,

researchers have focused on developing quality assurance standards to ensure the delivery of

treatment while using respiratory gating procedures.

30

Chapter III: Methodology

This research project examined left-sided breast cancer patients receiving radiation

therapy with the addition of respiratory gating technique. The study observed the dose to the

normal structures in a respiratory gating and non-respiratory gating plan. The interest in

performing the research stems from patients who were treated for breast cancer but later

developed cardiac toxicities due to the radiation the heart received during treatment. This chapter

will discuss the sample selection, instrumentation, data collected for analysis of the respiratory

gating study, and limitations of the research.

Sample Selection and Description

The patient population of left-sided breast cancer patients selected for this study was

compiled using a simple random sampling method. The study includes 10 patients chosen at

random who were treated for left-sided breast cancer at Gundersen Lutheran Medical Center for

radiotherapy with amplitude respiratory gating during January of 2011 to December of 2011. The

patient population was chosen at random to create a diverse group of patients with variable

breast, lung, and heart volumes. The research project consists of females who vary in age. This

study will compare the 2 data image sets (respiratory gating and non-respiratory gating) obtained

at simulation. The original treatment plan using the respiratory gating scan will be transferred to

the non-gating CT scan. The plan will be setup identical to the one used for treatment and

verified by checking the isocenter location via reference fields.

Instrumentation

The left sided breast cancer patients used for this research study were originally treated

with radiotherapy with the addition of respiratory gating. The CT images were captured with a

General Electric LightSpeed CT scanner. The respiratory gating system used for treatment was a

Varian RPM system. The RPM system is used to decrease the amount of artifact seen during a

patient’s breathing cycle and to measure motion.5 A Pinnacle3 Phillips version 8.0m treatment

planning computer was used to create the radiation treatment plans for both the respiratory gating

and non-respiratory image sets. The plans were computed with the heterogeneity correction

component turned on using the adaptive convolve algorithm. The patients were immobilized

with the use of a Vac-Lok and a wing board. Patients were scanned in the supine position with

their arms positioned above their head to decrease dose to normal structures and to ensure the

treatment volume would be covered effectively. The CT obtained did not include intravenous

contrast.

31

Data Collection Procedures

The data collected for the research study will come from the respiratory gating scan and

the non-respiratory gating scan obtained at the patient’s simulation. The plan created for the

patient’s treatment will be computed on each data set. The treatment plan will be transferred to

the non-respiratory gating scan and verified by checking that the location of the isocenter

matches that used in the respiratory gating scan. DRRs of the anterior and right lateral reference

fields of the original treatment plan on the gating scan will be compared to the anterior and right

lateral reference fields of the non-gating scan to make sure that isocenter is in the same location.

In order to evaluate the dose to the normal structures the following were contoured on

both data image sets: left lung, right lung, total lung, heart, and the left ventricle. The original

contours from the respiratory gating plan were used to record the research data. The left ventricle

was added to achieve more data for the analysis of respiratory gating in relationship to heart

tissue damage. Feng et al21 devised a cardiac atlas to aid in contouring the heart and

substructures. The Feng et al21 atlas was used to distinguish the left ventricle volumes in the

gating and non-gating scans. The total volume, the minimum, maximum and mean dose were

measured for the left lung, right lung, total lung, heart and left ventricle for the treatment plans

on the gating and non-gating scans.

Data analysis

After collecting the data from the gating and non-gating scan the analysis focused on the

dose to the heart and left ventricle. The dose to the left, right, and total lung was also monitored.

The percent volume of the lung receiving 20 Gy was measured and compared between the two

scans. The total lung volume between the gating and non-gating scans was measured. The

average mean dose for the total lung was recorded between scans. The average mean dose of the

heart and left ventricle were also compared amongst the gating and non-gating scan. After

evaluation of the dosimetric parameters, the results determined if respiratory gating for left-sided

breast cancer patients made a significant difference in treatment delivery.

Limitations






32











Summary

For this retrospective study, 10 left-sided breast cancer patients were selected to analyze

the effects of respiratory gating during treatment. The radiation treatment plans were created on

respiratory gating and non-respiratory gating CT scans. Patients were treated in the clinic

according to the radiation treatment plan designed from the respiratory gating scan. A non-

respiratory gating scan was obtained at the initial CT-simulation. The respiratory gating

treatment plan was transferred to the non-respiratory gating scan. After contouring the normal

structures in the treatment field, heart, left ventricle, right lung, left lung, and total lung the

radiation exposure to the normal structures was recorded. The data was obtained to determine the

efficacy of respiratory gating in left-sided breast cancer patients.

33

Chapter IV: Results

Breast cancer patients are treated with radiation therapy to decrease the rate of

recurrence.5 Radiotherapy is a curative form of treatment for breast cancer patients. However,

radiotherapy recipients experience cardiac abnormalities that develop into heart disease later on

in life. In order to decrease the amount of radiation delivered to the heart during radiotherapy

treatment, respiratory gating is used. The purpose of this study was to determine the benefits of

respiratory gating in left-sided breast cancer patients. This research collected data from patient’s

treatment plans to evaluate the dosimetric treatment plan from the respiratory gating scan to a

treatment plan from a non-respiratory gating scan. The treatment plans compared the dose

distribution between the gating and non-gating treatment plan scans. To retrospectively analyze

the patients, the gating scan dosimetric plan was transferred to the non-gating scan treatment

plan, verified by orthogonal DRRs, and calculated. The data for this research was measured

through a comparison analysis of the dose delivered to the right and left lung, total lung, heart,

and left ventricle between the two treatment plan scans.

Item Analysis

Ten patients were used in the retrospective studies which are referred to as patients A

through J in the following results section. A total of 20 plans were reviewed, 10 dosimetric plans

on gating scans and 10 dosimetric plans on non-gating scans. The minimum dose, maximum

dose, mean dose, and percent dose received to specific volumes were compared to look at the

effects of radiation therapy. The primary focus of the study was to measure the amount of

radiation delivered to the heart and left ventricle. Additional areas of interest were the lung

volumes. Patients selected for the study had left-sided breast cancer so the dose to the recorded

dose to the right lung was minimal. The average mean dose delivered to the right lung for

patients A-J was 18.3 cGy for the dosimetric plan developed on the gating scan. The non-gating

scan dosimetric plan showed an average mean dose to the right lung for patients A-J as 17.5 cGy.

The percent difference between the gating and non-gating scan was 5% for the average mean

lung dose of the right lung volume.

The amount of dose delivered to the ipsilateral lung during breast radiotherapy is also

normally measured. The percent of lung volume receiving 20 Gy was recorded for both scans.

The percent of lung receiving 20 Gy in the gating scan for patients A-J was, 3.3%, 18.3%, 6.7%,

9.0%, 14.1%, 11.7%, 11.8%, 7.8%, 7.8%, 6.1%, and 25.9% respectively. The percent of lung

receiving 20 Gy in the non-gating scan for patients A-J was, 3.9%, 13.6%, 2.9%, 7.0%, 15.7%,

34

7.0%, 11.0%, 4.5%, 3.9%, and 25.7% respectively. The average percentage of the left lung

volume receiving 20 Gy for patients A-J in the gating scan was 11.5%. The average percentage

of the left lung volume receiving 20 Gy for patients A-J in the non-gating scan was 9.5%. Table

1 lists the values for the percent volume of ipsilateral lung receiving 20 Gy. Figure 1 is a graph

of the patient A- J demonstrating the difference between the gating and non-gating scan in terms

of the percent volume of the left lung receiving 20 Gy.

The respiratory and non-respiratory gating scan demonstrated a difference between the

total lung volumes. The respiratory gating scan showed an average total lung volume of 3500.81

cm3. The non-respiratory gating scan showed an average total lung volume of 2701.8 cm3. Table

3 lists the values of the average total lung volume (cm3) for the gating and non-gating scans. The

percent difference between the two scans is 30 percent. The average mean total lung dose for the

respiratory gating scan was 298.53 cGy. The average mean total lung dose for the non-

respiratory gating scan was 258.73 cGy. The percent difference for the mean total lung dose was

15.4% between the respiratory gating and non-respiratory gating scan. Figure 2 displays the

average mean total lung dose for the gating and non-gating scans. Table 2 lists the values for the

average mean total lung (cGy) for the gating and non-gating scans.

The heart and left ventricle volumes in the gating and non-gating scans were measured to

determine the amount of radiation delivered during patient treatment. The mean heart doses for

the gating and non-gating scans for patients A-J are shown in a graph format in Figure 3. The left

ventricle doses for the gating and non-gating scans for patients A-J are shown in a graph format

in Figure 4. The mean heart and left ventricle dose was higher in 7 out of 10 patients when gating

was not used in the radiation therapy planning. Table 4 lists the average mean dose for the heart

and left ventricle for the gating and non-gating scans.

To compare the different image data sets, the average mean dose to the heart and left

ventricle were calculated. The average mean heart dose for the respiratory gating scan was 99.87

cGy. The average mean heart dose for the non-respiratory gating scan was 115.34 cGy. The

average mean left ventricle dose for the respiratory gating scan was 161.08 cGy. The average

mean left ventricle dose for the non-respiratory gating scan was 203.24 cGy. The average mean

heart dose between the respiratory and non-respiratory gating scan results in a 15.5 percent

change. The average left ventricle heart dose between the respiratory and non-respiratory gating

scan results in a 17.7 percent change. Figure 5 depicts the values obtained for the average mean

dose of the heart and left ventricle in the gating and non-gating scan.

35

Overall, the retrospective study showed that the respiratory gating procedure decreased

the dose to the heart and left ventricle in the patients selected for the study. The total volume of

lung treated increased when respiratory gating was used. The ipslateral lung showed a slight

increase when measuring the percent volume of lung treated at 20 Gy. Dose to the right lung in

both the gating and non-gating scans was minimal because radiation was delivered to the left-

side only. Tables 5-24 list the volume (cm3), minimum dose (cGy), maximum dose (cGy), and

mean dose (cGy) for the right lung, left lung, total lung, heart, and left ventricle volumes.

36

Chapter V: Discussion

Breast cancer patients being treated with radiotherapy are at an increased risk for

developing cardiovascular disease after surviving breast cancer. Respiratory gating is a

procedure used to decrease the dose delivered to the heart during breast radiotherapy treatments.

Limiting the amount of radiation exposure to the patient’s heart decreases the likelihood a patient

will develop heart disease later on in life. Borger et al26 reported an increase in cardiovascular

disease in patients treated for left-sided breast cancer patients compared to right-sided breast

cancer patients. Researchers have employed different techniques to reduce the damage to the

heart during radiotherapy of left-sided breast cancer patients. McIntosh et al24 demonstrated how

VDIBH can be used to decrease the radiation exposure to the LAD coronary artery and the heart

by increasing the displacement between the breast target and heart. Different treatment planning

techniques have been explored to create the optimal treatment plan for left-sided breast cancer

patients. Tan et al14 studied IMRT planning objectives in order to develop treatment plans that

reduced the radiation exposure to the heart in left-sided breast cancer patients. The researchers

found that when the IMRT plan was optimized using AMT and H + LV as planning objectives

there was a decrease to the mean dose to the heart, LV, and AMT compared to using the heart

alone.14 Three dimensional conformal radiation therapy is another form of treatment planning

that has been shown to decrease the radiation exposure to the heart in left-sided breast cancer

patients.5 This research paper measured the effects of the organs at risk for breast radiotherapy

for plans created on respiratory gating and non-respiratory gating scans. This study evaluated the

radiation delivered to the right lung, left lung, total lung, heart and left ventricle. Data analysis

included measuring the amount of radiation delivered to the ipsilateral lung during radiation

treatment by recording the percent of lung volume that received 20 Gy. The average percentage

of the left lung receiving 20 Gy for treatment plans created on the gating scan was 11.5% and on

the non-gating scan was 9.5%. The heart and left ventricle volumes were also analyzed. The

average mean heart dose for the gating scan was 99.87 cGy whereas the average mean heart dose

for the non-gating was 115.34 cGy. The average mean left ventricle dose for the gating scan was

161.08 cGy where as the average mean left ventricle dose for the non-gating scan was 203.24

cGy. Seven out of 10 patients from the sample selection had a decrease in the amount of

radiation delivered to the heart and left ventricle.

37

Limitations
















Conclusions

After collecting the data and performing calculations, this study determined that left-

sided breast cancer patients may see positive benefits when being treated with respiratory gating

procedures. This study showed that seven out of 10 patients demonstrated a decrease in the

amount of radiation delivered to the heart and left ventricle. There was a 15.5% decrease in the

average mean dose of the heart. The left ventricle showed a 17.7% decrease in the average mean

dose. A study done by Korreman et al28 also confirmed the use of respiratory gating in left-sided

breast cancer patients to decrease the dose to the heart.

Although, there was a decrease in the mean dose to the heart and left ventricle the

respiratory gating treatment showed an increase of total lung volume treated. An increase of

15.4% of total lung volume was treated when using the respiratory gating procedure. These

results are contrary to a study done by Korreman et al28 which showed a decrease in pneumonitis

for patients that used the DIBH and IG methods and respiratory gating. The DIBH and IG

methods were used by Korreman et al28 to decrease the inspiration during the respiratory gating.

Although, there was an increase in total lung being treated in the respiratory gating scan the

radiation delivered to the lung was considered acceptable by the radiation oncologist treating the

38

patient. The heart and left ventricle were the main focus of this study because of the heart

toxicities a patient may experience later on in life due to the radiation treatment. On average,

there was a clear advantage to using respiratory gating in the left-sided breast cancer patients

used in the study.

Recommendations

The research study provided a limited sample size. In future studies involving respiratory

gating a larger sample size is needed to provide more accurate results. Another recommendation

to improve the study would include the addition of the target area. Including the target volume

would help determine if and how respiratory gating is affecting the target volume proximal

normal structures. Three of the 10 patients used in this retrospective study did not receive the

benefits of the respiratory gating procedure, which should be analyzed to determine if it was due

to the plan transfer performed between the 2 scans or if it was related to anatomical differences

among the patients chosen. Along with monitoring dose in 3DCRT plans it is also imperative to

determine how the use of IMRT in breast radiotherapy reduces the amount of dose delivered to

OR and increases the efficacy of the patient’s treatment plan. Analyzing planning objectives to

reach an optimal plan is an important part of developing the treatment planning process for left-

sided breast cancer patients.

39

Tables

Table 1. Percent volume of left lung receiving 20 Gy Patient Gating Scan Non-Gating Scan A 3.30% 3.90% B 18.30% 13.60% C 6.70% 2.90% D 9.00% 7.00% E 14.10% 15.70% F 11.70% 7.00% G 11.80% 11.00% H 7.80% 4.50% I 6.10% 3.90% J 25.90% 25.70% Average % 11.50% 9.50%

Table 2. Average mean total lung (cGy) gating vs. non-gating scan Scan Average Mean Total Lung (cGy) Gating 298.53 Non-Gating 258.73 % Difference 15.4%

Table 3. Average total lung volume (cm^3) gating vs. non-gating scan Scan Average Total Lung Volume (cm^3) Gating 3500.81 Non-Gating 2701.8 % Difference 0.3

Table 4. Average mean dose for the heart and left ventricle for the gating and non-gating scans. Average Mean Dose (cGy) Scan Heart Left Ventricle Gating 99.87 161.08 Non-Gating 115.34 189.53 % Difference 0.155 0.177

40

Table 5. Patient A gating scan treatment plan results

Structure Volume (cm^3)

Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 2006.16 5.9 204.5 25.1 Lt Lg 1545.35 13.4 5153.3 281.4 T Lg 3551.74 5.9 5153.3 136.6 Heart 736.83 21.4 1439.7 120.3 Lt Vent 190.1 45.1 1253 180.9

Table 6. Patient A non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1681.4 6.3 194.4 26.6 Lt Lg 1283.5 14.5 5123.4 303.3 T Lg 2965.03 6.3 5123.4 146.3 Heart 734.74 29.9 2503.4 135.4 Lt Vent 191.89 43.6 2109.2 188.6

Table 7. Patient B gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1946.99 4.1 1021.4 23.6 Lt Lg 1710.88 8.9 5504.4 992 T Lg 3658.02 4.1 5504.4 476.6 Heart 598.7 18.8 4377.1 134.1 Lt Vent 194.89 33.7 4019 220.5

Table 8. Patient B non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1487.95 4 139.2 21.2 Lt Lg 1245.87 9.4 5308 791.8 T Lg 2734.11 4 5308 372.4 Heart 603.24 15.1 3233.5 114 Lt Vent 214.19 30.8 2562.9 177.8

41

Table 9. Patient C gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 2149.29 1.8 215.2 14.3 Lt Lg 1886.78 6.5 4481.7 379.4 T Lg 4048.36 1.8 4481.7 185 Heart 668.69 15.5 2130 89.7 Lt Vent 185.3 18.6 2051 136.3

Table 10. Patient C non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1380.25 1.8 95.4 11.6 Lt Lg 1347.16 Not on DVH 4699.9 224.5 T Lg 2717.82 1.8 4699.9 117.2 Heart 645.04 10.6 1481.8 75.7 Lt Vent 177 24 1605.9 124.3

Table 11. Patient D gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)


Table 12. Patient D non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1645.86 3.8 134.9 16 Lt Lg 1241.38 12.8 4888.5 405.6 T Lg 2887.62 3.8 4888.5 183.5 Heart 616.1 20.2 4804 191.7 Lt Vent 224.64 31.9 4779.2 316.7

42

Table 13. Patient E gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 2015.66 1.5 335.7 15.2 Lt Lg 1818.12 3.7 5444.4 761.3 T Lg 3838.73 1.5 5444.4 369 Heart 605.3 10.7 1115.1 58.1 Lt Vent 171.91 17.2 1008.2 95.7

Table 14. Patient E non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1746.27 3 359.4 15.5 Lt Lg 1563.85 5.3 5439.1 830 T Lg 3310.38 3 5439.1 400.4 Heart 597.48 10.6 1511.4 65.3 Lt Vent 177.54 16.2 1794.2 115.2

Table 15. Patient F gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1487.91 3.7 353.7 18.7 Lt Lg 1300.93 7 5164.2 622.2 T Lg 2789.08 3.7 5164.2 300.3 Heart 637.54 16.3 4319.8 114.4 Lt Vent 196.5 27.8 4072.1 211.1

Table 16. Patient F non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1172.7 3.5 224.6 18.5 Lt Lg 1087.82 8.2 4819.6 426.6 T Lg 2260.79 3.5 4819.6 214.9 Heart 581.22 18.4 4590 134.9 Lt Vent 169.65 28.4 4660.7 252.3

43

Table 17. Patient G gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1876.64 2.3 187.8 16.3 Lt Lg 1465.24 6 5380.7 672.8 T Lg 3341.3 2.3 5380.7 304.3 Heart 573.15 17 3655 118.7 Lt Vent 148.39 29.7 3680.2 217.8

Table 18. Patient G non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1540.98 2.3 203.1 16.6 Lt Lg 1137.36 7.7 5281.6 621.3 T Lg 2678.47 2.3 5281.6 273.4 Heart 528.96 19.1 4434 158.1 Lt Vent 153.99 33.1 4501.6 283.8

Table 19. Patient H gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)


Table 20. Patient H non-gating scan treatment plan results Structure Volume (cm^3) Minimum Dose (cGy) Maximum Dose (cGy) Mean Dose (cGy) Rt Lg 759.14 3.6 147.9 10.5 Lt Lg 935.74 5.7 4780 311.8 T Lg 1694.91 3.6 4780 138.2 Heart 403.29 16.6 4051 104.1 Lt Vent 137.29 23.3 2843.6 167.5

44

Table 21. Patient I gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 2575.95 1.6 142.2 19.9 Lt Lg 2098.69 1.3 5102.9 375.9 T Lg 4684.28 1.3 5102.9 179.7 Heart 691.4 11.7 520.1 55.9 Lt Vent 189.89 16.4 479.6 80

Table 22. Patient I non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1625.03 4 89.4 18.3 Lt Lg 1441.66 0.2 5112.9 257.9 T Lg 3067.15 0.2 5112.9 130.9 Heart 686.77 16.3 4614.8 77.3 Lt Vent 193.44 19.7 3876.3 126.5

Table 23. Patient J gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1433.66 8.5 246.2 22.1 Lt Lg 610.1 24.5 5238.3 1288 T Lg 3422.61 8.5 5238.3 600.6 Heart 535.91 27.4 1034.8 102.5 Lt Vent 163.48 42.9 972.2 149.1

Table 24. Patient J non-gating scan treatment plan results


Minimum Dose (cGy)

Maximum Dose (cGy)

Mean Dose (cGy)

Rt Lg 1105.1 9.3 194.2 19.9 Lt Lg 1596.21 26.6 5270 1285.7 T Lg 2701.49 9.3 5270 610.1 Heart 533.58 21.4 2549.1 96.9 Lt Vent 168.52 38.7 1531.4 142.6

45

Figures

46

47

48

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Documents

Benefits, Disadvantages, and Challenges of Respiratory Gating