Scientific Abstract 3645; Table Median Dose per fraction

ABS Point T&O SRA

A (right) 7.0 (5.8-7.7) 7.0 (5.9-7.6)A (left) 7.0 (6.1-7.8) 7.0 (6.0-7.4)B (right) 1.9 (1.0-2.7) 2.0 (1.3-7.0)B (left) 2.0 (1.2-3.6) 2.0 (1.0-2.9)P (right) 1.7 (0.9-9.3) 1.5 (0.8-12.2)P (left) 1.8 (1.0-5.2) 1.4 (0.0-3.2)Bladder 4.8 (0.0-8.6) 5.9 (2.3-9.7)Rectum 4.0 (1.6-6.8) 4.6 (2.8-6.4)

Volume 90 � Number 1S � Supplement 2014 Poster Viewing Abstracts S857

3644Integrated Deformable Registration and Biologic Modeling toCompare Dose Distributions of High-Dose IMRT and CombinationIMRT-Brachytherapy (Combo-RT) in Localized Prostate CancerJ. Raince, A.C. Riegel, H. Chou, A. Halthore, L. Potters, and B. Cox;

NSLIJ Health System, New Hyde Park, NY

Purpose/Objective(s): An emerging body of evidence suggests that

combo-RT offers superior biochemical control and distant metastasis free

survival for patients with intermediate-risk prostate cancer when compared

to dose escalated IMRT alone. However, current studies do not sufficiently

consider the potential impact of patient-specific integrated dosimetry on

reported clinical outcomes. In this study, we integrate deformable regis-

tration and biologic modeling to compare the equivalent doses given in 1.8

Gy (EQD 1.8) for patients receiving combo-RT vs IMRT alone.

Materials/Methods: 20 patients receiving IMRT (to a prescribed total dose

of 81 Gy) and 20 patients receiving combo-RT (IMRT prescribed dose of

50.4 Gy and LDR brachytherapy boost with Pd-103 to 100 Gy) during the

time period of January 1, 2012 to December 31, 2013 were retrospectively

analyzed. Post-implant CT scans were registered to EBRT simulation CT

scans via multi-pass B-spline deformable registration. Deformable trans-

formations were applied to the brachytherapy dosimetry and converted to

1.8 Gy equivalent dose for summation with the IMRT component. To

compute equivalent dose, we used a/b ratio Z 3 for prostate cancer and

late responding normal tissues (rectum and bladder). The EQD 1.8 of

combo-RT vs IMRTalone for prostate, bladder maximum (max) point dose

and rectal max point dose were calculated.

Results: A statistically significantly greater mean prostate dose of 153.01

Gy vs 82.98 Gy (p <0.0001), mean bladder max point dose of 185.31 Gy

vs 85.08 Gy (p Z 0.0007) and mean rectum max point dose of 157.22 Gy

vs 84.32 Gy (p Z 0.0002) were found for the combo-RT compared to

IMRT alone cohort, respectively.

Conclusions: This study integrates deformable registration and biologic

modeling to determine the cumulative equivalent dose distributions for

men treated for localized prostate cancer with various modalities. Our

preliminary analysis demonstrates that combo-RT offers superior dose

escalation compared to IMRT alone but higher maximum point doses to

adjacent normal tissues. We plan to use this patient-specific, spatially

registered, and biologically reconstructed dosimetry technique to assess

toxicities and clinical outcomes of patients treated with combo-RT in

future analyses.

Author Disclosure: J. Raince: None. A.C. Riegel: None. H. Chou: None.

A. Halthore: None. L. Potters: None. B. Cox: H. Speakers Bureau; Bayer

Pharmaceuticals. K. Advisory Board; Bayer Pharmaceuticals.

3645Dosimetric Comparison Between Split Ring and Tandem & OvoidHDR Brachytherapy Applicators in Cervical Cancer TreatmentO. Ishaq,1 J.R. Montgomery,2 T. Duckworth,1 H. Hsu,1 and P.B. Schiff1;1New York University Medical Center, New York City, NY, 2Johns Hopkins

University Department of Surgery, Baltimore, MD

Purpose/Objective(s): HDR brachytherapy boost is an integral part of

definitive chemoradiation treatment for cervical cancer. The boost is

commonly delivered using tandem and ovoids but other brachytherapy

applicators are also available. The split ring applicator (SRA) is a newer

applicator with a tandem and two half rings offering a wide range of

implantation and dwell configurations. However, there is no published

comparison of dosimetric differences between the SRA and T&O

applicators.

Materials/Methods: 50 consecutive patients with FIGO Stage IB1-IVA

were treated at one institution with definitive chemoradiation between

2010 and 2014. Patients received whole pelvis EBRT to 45Gy +/- para-

metrial boost to 50.4-54Gy. Following EBRT, patients received afterloaded

Ir-192 HDR brachytherapy boost of 28Gy in 4 fractions over two weeks

prescribed to Point A. Each week T&O or SRA was inserted in the

operating room followed by two consecutive daily HDR treatments. 21

patients were treated with T&O, 23 with SRA, and 6 with T&O and SRA

(different applicator each week). Absolute doses were calculated for ABS

reference points: A, B, P, Bladder and Rectum. Multivariate Analysis of

Variance (MANOVA) was conducted using applicator type as the inde-

pendent variable and dose at ABS reference points as dependent variables.

Results:MANOVA results using the Wilks Lambda distribution revealed a

statistically significant difference between the SRA and T&O groups, F Z3.65, p Z 0.001. Univariate analysis revealed no significant difference in

Point A, B left, or P right. There was a statistically significant difference in

dose at B right (F Z 4.38, p Z 0.039), P left (F Z 4.27, p Z 0.042),

Bladder (F Z 14.05, p Z <0.001), and Rectum (F Z 8.97, p Z 0.004).

Separate MANOVA analysis for the 6 patients who had treatments with

both applicators (n Z 6) revealed no significant difference in dose dis-

tribution between the two applicators, F Z 0.84, p Z 0.8.

Conclusions: Comparison of the two applicators reveals a possible in-

crease in dose to the bladder and rectum with the SRA compared to T&O.

However, in patients treated with both applicators this difference was not

observed suggesting that patients’ individual anatomy may be the driver of

the difference detected. Alternatively, a statistically significant difference

may not be seen in such a small subset of patients. Dose distributions in a

larger cohort along with toxicity outcomes are needed to resolve the

clinical implications of any differences.

Author Disclosure: O. Ishaq: None. J.R. Montgomery: None. T. Duck-

worth: None. H. Hsu: None. P.B. Schiff: None.

3646Toward Developing Survivorship Care Plans for Breast CancerPatients at High Risk for Radiation-Related Cardiac EffectsR.M. Howell, W. Tereffe, M.C. Stauder, F. Stingo, E.A. Strom,

G.H. Perkins, B.D. Smith, W.A. Woodward, K.E. Hoffman, T.A. Buchholz,

M.R. Salehpour, S.F. Kry, C.H. Barcenas, W.S. Yusuf, and S. Shaitelman;

M.D. Anderson Cancer Center, Houston, TX

Purpose/Objective(s): Radiation therapy (RT) for left-sided breast cancer

is associated with some risk of cardiac toxicities but the risk varies ac-

cording to RT technique used and treating institution. Furthermore, there

are no guidelines regarding the definition of a “high” heart dose or se-

lection criteria for survivorship follow-up. Thus, the objectives of this

study were to define typical heart doses and calculate the predicted relative

risk (PRR) of RT-related major coronary events for each of the standard RT

techniques used at our institution, and quantitatively identify patients with

atypically high heart dose and PRR.

Materials/Methods: We evaluated heart doses for consecutively treated

patients who underwent RT (prescribed dose of 40.05 to 54.00 Gy) for a

primary left-sided breast cancer from November 2013 to December 2014.

The PRR of developing RT-related major coronary event was calculated

using mean heart dose and a breast cancer specific dose response model

from the literature. Patients were classified by RT technique: tangent fields

only (T); tangent and supraclavicular fields (T+SC); tangent, supra-

clavicular, and internal mammary chain fields (T+SC+IMC); prone breast;

and electron chest wall (ECW). Clinical data were abstracted: age at RT,

body mass index (BMI), use of deep inspiration breath hold (DIBH),

cardiac risk factors, and receipt of cardiotoxic chemotherapy. Analysis of

Scientific Abstract 3646; Table Mean � SD (data for initial course of RT and does not include boost)

All [N Z 291] T [N Z 119] T+SC [N Z 8] T+SC+IMC [N Z 158] Prone [N Z 3] ECW [N Z 3]

increased PRR (%) 16.4�15.8 4.4�2.1 10.3�7.4 26.0�15.6 2.6�0.4% 20.1�14.2dosemean (Gy) 2.2�2.1 0.6�0.3 1.4�1.0 3.5�2.1 0.4�0.1 2.7�1.9Age at RT 54.8�11.8 58.1�9.7 53.8�12.0 52.6�11.5 66.0�14.0 37.5�27.8BMI 29.8�6.2 29.5�6.3 33.2�4.6 29.9�6.1 35.5�7.1 26.8�3.4Prescription (Gy) 48.3�3.6 46.0�4.3 50.5�1.3 50.1�1.1 43.4�4.7 50.0�0.0

International Journal of Radiation Oncology � Biology � PhysicsS858

variance (ANOVA) was used to assess the effect of treatment type on mean

heart dose and PRR.

Results: The 291 left-sided RT patients had a mean age at RT of 54.8 years

�11.8 and BMI of 29.8�6.2. Of those patients, 62% had at least 1 cardiac

risk factor, 67% received chemotherapy, and 86% treated using DIBH.

ANOVA demonstrated significant difference in mean heart dose according

to treatment type (see Table); multiplicity adjusted p-values < 0.05. The

highest risk category was T+SC+IMC; The upper 95% confidence interval

from this category (PRR Z 28%, mean heart dose Z 3.8 Gy) was defined

as our “internal” benchmark for high mean heart dose and PRR. A total of

50 patients (17%) in this study were above this level.

Conclusions: This study evaluated heart doses for 291 patients who

received left sided breast RT and identified an internal benchmark for a

high mean heart dose and PRR. Our long-term objectives are to assess

correlation between heart dose and pre-existing cardiac risk factors and to

prospectively identify patients at high risk for RT-related cardiac effects to

define patient specific survivorship care plans.

Author Disclosure: R.M. Howell: None. W. Tereffe: None. M.C.

Stauder: None. F. Stingo: None. E.A. Strom: None.G.H. Perkins: None.

B.D. Smith: E. Research Grant; Co-investigator, Varian Master Research

Agreement with M.D. Anderson Cancer center. W.A. Woodward: None.

K.E. Hoffman: None. T.A. Buchholz: None.M.R. Salehpour: None. S.F.

Kry: None. C.H. Barcenas: None. W.S. Yusuf: None. S. Shaitelman: E.

Research Grant; Principal investigator: Elekta Research Grant.

3647Rapid Evaluation of Radiation Therapy Response Using Multi-Parametric Image TreemapsE.S. Paulson and D.E. Prah; Medical College of Wisconsin, Milwaukee, WI

Purpose/Objective(s): Utilization of multi-parametric images for evalu-

ation of treatment response can be time consuming and overwhelming.

Treemaps are a new class of intuitive data visualization techniques for

rapidly evaluating large amounts of time-varying data, particularly in

financial services applications. The goal of this work was to investigate

whether treemaps offer advantages for evaluating response to radiation

therapy (RT).

Materials/Methods: A retrospective, proof-of-principle study was per-

formed on three patients with soft tissue sarcomas. Diffusion-weighted

(DW) and dynamic contrast-enhanced (DCE) images were acquired on a

3T MRI prior to and four weeks after RT. Pre and post-RT DW and DCE

parameter maps (e.g., ADC, Ktrans, kep, ve, vp) were generated for each

patient. Tumor regions of interest were constructed using DT1 maps.

Treemaps were generated using average parameter values obtained

within the tumor region of interest. The treemap is a color-coded, equal-

aspect, 2D array containing nested cells for each parametric map. The

area of each cell represents the percent change of a given parameter

relative to its pre-treatment value. The color of each cell indicates the

direction of percent change. For example, if ADC increased 5% post-

treatment, the cell would be colored green; if ADC decreased 5% the cell

would be colored red; and if there was no change in ADC, the cell would

remain black.

Results: Ktrans demonstrated the largest cell area with color green,

indicating the greatest percent reduction between pre-/post RT. Ve

demonstrated the smallest cell area with color green, indicated the

smallest percent increase between pre-/post-RT. Ideally, treemaps would

be generated on a voxelwise basis and displayed as a photomosaic

parameter map. However, due to changes in overall patient size over the

course of treatment, generation of voxelwise treemaps was not possible,

and a single treemap was generated using parametric values averaged

over the pre-/post-RT tumor structures. Treemaps have the advantage of

displaying two parameters (e.g., percent change and direction) simul-

taneously for each parametric map on the same plot. This has the

advantage of rapidly summarizing multi-parametric data, which could be

especially useful for frequent response evaluations in patient-tailored

adaptive radiation therapy. These results suggest a natural human factors

advantage of treemaps over conventional multi-parametric image

analysis.

Conclusions: We have introduced a novel method for rapidly evaluating

treatment-induced changes in multi-parametric images using treemaps.

Future work will explore the use of voxelwise multi-parametric treemaps

for target delineation in radiation treatment planning.

Author Disclosure: E.S. Paulson: None. D.E. Prah: None.

3648Study on the Sensitivity of Gamma-Index Evaluation Methods toPositioning Errors of High-Definition MLC of True Beam STx inVMAT Quality Assurance for SBRTS. Hwang,1 S. Ye,2,1 J. Park,1 and J. Kim1; 1Department of Radiation

Oncology, Seoul National University Hospital, Seoul, Korea, Republic

of Korea, 2Program in Biomedical Radiation Sciences, Department of

Transdisciplinary Studies, Graduate School of Convergence Science

and Technology, Seoul National University, Seoul, Korea, Republic of

Korea

Purpose/Objective(s): To assess the sensitivity of gamma-index evalua-

tion methods to intentional error within arc dynamic tolerance levels of

high definition multi-leaf collimator (HD MLC) in volumetric modulated

arc therapy (VMAT) quality assurance (QA) for stereotactic body radiation

therapy (SBRT).

Materials/Methods: 10 patients diagnosed with Lung cancer and 10

patients diagnosed with localized spine metastasis were selected.

VMAT plans were generated using EclipseTM TPS with 6 MV flat-

tening filter free (FFF) beam for lung SBRT while 10 MV FFF beam

for spine SBRT. Truebeam STx with HD-MLC was used for delivery.

MLC positions in VMAT plans were modified with in-house program,

which 3 types of MLC errors were introduced to each VMAT plan.

The first type was a simulation of both MLCs were opened by 0.25

mm, 0.5 mm, 1 mm and 2 mm in an isoplane leading to a larger

opening of MLC apertures (Class Out). The second type was a

simulation of both MLCs were closed by 0.25 mm, 0.5 mm, 1 mm

and 2 mm leading to a smaller opening of MLC apertures (Class In).

The third type was intended to simulate the effect of gravitational

forces on MLCs. Both MLC banks were shifted in the same direction

toward ground according to the gantry angle by 1 mm, 2 mm and 3

mm (Class Shift). The planar dose distributions of each plan were

measured with MapCHECK2 detector array and EBT2 film. The

gamma evaluation was performed with criteria of 1%/1 mm, 1.5%/1.5

mm, 1%/2 mm, 2%/1 mm and 2%/2 mm. The passing rate of each

criterion vs the magnitude of MLC misalignment was evaluated. The

dose volume histograms (DVHs) of original VMAT plans were

compared to those of modified VMAT plans. The correlation between

gamma passing rate of each criterion and dose-volumetric changes in

target volume has been investigated.