RADIOTHERAPY

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Patients getting radiation to the head may need a mask. The mask helps keep the head from moving so that the patient is in the exact same position for each treatment.

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Radiation?Photons:•All forms of electromagnetic radiation (light, x-ray, gamma) are actually packaged and delivered in the form of many many small units of energy, the photons.

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What is radiation therapy?• High-energy radiation to shrink tumors

and kill cancer cells.• X-rays, gamma rays, • Charged particles are types of radiation

used for cancer treatment.• The radiation may be delivered by a

machine outside the body external-beam radiation therapy),

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Brachytherapy

• Radioactive material placed in the body near cancer cells internal radiation therapy, also called brachytherapy). • Placement of a radioactive material

inside the body.

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Systemic Radiation Therapy• Systemic radiation therapy uses

radioactive substances, such as radioactive iodine, that travel in the blood to kill cancer cells.• Half of all cancer patients receive

some type of radiation therapy sometime during the course of their treatment.

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How does radiation therapy kill cancer cells?

Radiation therapy kills cancer cells by damaging their DNA directly

Or

Indirectly create charged particles (free radicals) within the cells that can in turn damage the DNA.

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• Cancer cells with damaged DNA is beyond repair stop dividing or die.

• Damaged dead cells are broken down and eliminated by the body’s natural processes.

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Does radiation therapy kill only cancer cells?

• Radiation therapy can also damage normal cells, leading to side effects.• Potential damage to normal cells into

account when planning a course of radiation.

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Thyroid Cancer• Radioactive iodine (RAI) is often

chosen for treatment of thyroid Cancer • Or hyperthyroidism (overactive

thyroid).• It is given in a single dose.

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Radioactive Iodine Treatment• RAI treatment is based on the fact that

the thyroid actively accumulates iodine, which it uses to produce thyroid hormones required for normal body function. • This RAI is like the iodine found in

foods such as fish, seaweed, and iodized salt.

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• except that it releases an electron, or beta particle, which creates its therapeutic action.• RAI is given dissolved in water or as a

capsule. • It is absorbed quickly by the stomach

and intestines12

• Carried in the bloodstream to the thyroid, where it is taken up by the gland.

Dose:• In the thyroid gland, the RAI disrupts

the function of some of the thyroid cells - the more radioactive iodine given, the more cells cease to function. 13

• As the cells stop functioning, excessive amounts of thyroid hormones are no longer produced, and symptoms of hyperthyroidism begin to disappear.

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Side Effects• A sore throat may occur a few days

after the treatment, which can be treated with acetaminophen. • Rarely, the salivary glands may swell,

which is caused by the iodine and not the radioactivity. • Some physicians believe that sucking

hard candies for a few days can prevent this. 15

• Mild nausea may develop for a few hours after the iodine is taken, so it is best not to eat two hours before and two hours after the iodine administration.

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Precautions• Some precautions are necessary

because of the small amount of radiation that emanates from the neck where the RAI is stored for a few days after treatment. While this radiation is

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Total Photons, A Measure of Radioactivity

Measure the radioactivity of a sample is to count the photons that are emitted.

Proper calibration factors:the counts per minute (CPM) can be converted into units of radioactivity, curies or becquerels.

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Exposure & Dose

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X-RAY unit•“Three Rs", roentgen, rad , rem•All of these were very practical units and have served their purpose well.

Gary “SI” Unit:Radiation dose expressed in terms of absorbed energy per unit mass of tissue.

Gray replaced “rad”1 gray= 1 joule/kilogram 22

• The amount of radiation that normal tissue can safely receive is known for all parts of the body.• Doctors use this information to

help them decide where to aim radiation during treatment.

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• CT scans are often used in treatment planning for radiation therapy. • During CT scanning, pictures of the inside of

the body are created by a computer linked to an x-ray machine.

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Why do Patients Receive Radiation Therapy?

Radiation therapy is sometimes given with curative intent (that is, with the hope that the treatment will cure a cancer, either by eliminating a tumor, preventing cancer recurrence, or both).

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• Radiation therapy may be used alone or in combination with surgery, chemotherapy, or both.• Radiation therapy may also be given

with palliative intent. Palliative treatments are not intended to cure. • Instead, they relieve symptoms and

reduce the suffering caused by cancer. 26

Examples of palliative radiation therapy are:

–Radiation given to the brain to shrink tumors formed from cancer cells that have spread to the brain from another part of the body (metastases).–Radiation given to shrink a tumor that is

pressing on the spine or growing within a bone, which can cause pain.

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• Radiation given to shrink a tumor near the esophagus, which can interfere with a patient’s ability to eat and drink.

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Exposure & Dose

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Intensity-modulated radiotherapy—what is it?

• Intensity-modulated radiotherapy (IMRT) is advanced technique in oncology • Improvements in computer technology

and imaging techniques

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• An ideal radiotherapy treatment delivers a high dose of radiation to the tumour but minimal dose to the surrounding normal tissue.• There is a clear relationship between

radiation dose and the probability of tumour control.• but the tumour dose is often limited

by the radiation tolerance of surrounding structures. 31

Three-dimensional Techniques

• The first step in planning a radiotherapy treatment is the accurate definition of the target volume.

• Example of a patient with prostate cancer who is to have both pelvic lymph nodes and the prostate gland irradiated.

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Conventional Conventional radiotherapy defines the area to be treated in relation to bony landmarks

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Conformal radiotherapy• CT scanning improve CR• Tumour is identified and drawn onto

each cross-sectional image creating a reconstructed three dimensional target volume. • The radiation beams are then shaped

to fit this volume and to provide shielding to the normal tissues.

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Conformal radiotherapy

• Routine use for the treatment of tumour sites including head and neck, brain, lung, prostate and bladder cancer

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• Conformal dose colour-wash. The target volume is contoured in white. The high dose region (red) is brick-shaped and includes part of the bladder.

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• Reduction in toxicity due to the improved conformity has been confirmed in clinical studies.• randomised patients with prostate

cancer between conformal and conventional radiotherapy.• Long term rectal toxicity was reduced

from 15% to only 5%.• Ref: Dearnaley et al.

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• Reduction in morbidity has enabled the use of escalating dose to treat prostate cancer.• Investigators at Memorial Sloane

Kettering Hospital:• increased the prescribed dose from 64

to 81 Gy resulting• in improved tumour control but an

increased risk of toxicity. 38

• To treat with these high doses, it is necessary• to further reduce the volume of

rectum irradiated. • This would only be possible with the

introduction of IMRT.

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Intensity-Modulated Radiotherapy

• IMRT is an advanced form of three-dimensional conformal radiotherapy. • It is of particular value for target

volumes with concave or complex shapes with close proximity to radiosensitive normal structures.

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It has two key additional:

1. Non-uniform intensity of the radiation beams.2. Computerised inverse planning

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Each beam is subdivided into hundreds of beamlets, each with an individual intensity.

Variable radiationintensity is generated across each beam

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• Variable radiation intensity is generated across each beam, in contrast to the uniform intensity • Level, enabling a very complex pattern

to be constructed

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• The use of several beams build up a highly conformal dose distribution,

• allowing precise shaping to a curved target and thus further sparing

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Advantages of IMRT• Improved target conformity, particularly for concavetarget volumes• Can produce intentional dose in homogeneity—dosepainting• Increases normal tissue sparing• Enables dose escalation• Can compensate for missing tissue.

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Disadvantages of IMRT

• Increased clinician time for target and organ outlining• Needs extensive quality assurance programme• Increased machine treatment time• Increased planning time (initially)• Increased total body irradiation dose. 46

Inverse planning

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Post-operative Breast cancer Radiotherapy

• Significant benefits in local control and survival, • long-term Radiotherapy have shown

increased side effects: • cardiac disease, • lung damage, • Breast distortion, rib fractures and pain.

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IMRT can improve

• the dose uniformity by compensating for missing tissue• and consequently improves the

cosmetic outcome. It is• possible to boost the tumour bed

using IMRT, and this

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