basic principles of radiation oncology

8/2/2019 Basic Principles of Radiation Oncology

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Bachtiar MurtalaDept of Radiology

Medical FacultyHasanuddin University

Makassar


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General consideration in choosing modalities in

the treatment of cancer : Surgery, for a lesion that can be technically removed

Irradiation, for a localized lesion in which surgerymay cause anatomically or physiologically undesirablesequelae and for a more extensive lesion notamenable to a surgical resection

Chemotherapy, for the treatment of micrometastases,chemosensitive tumors, disseminated disease


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Some limitations of surgery

Inadequate removal of gross tumor

Inadequate resection of microextension Undetected metastases to regional lymph node

Systemic micrometastases


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Some limitations of chemo Tumor cell burden

Variation of cell sensitivity

Chemoresistance Side effects


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DefinitionRadiation oncologyis a clinical specialty dealingwith the use of ionizing radiation ( electromagnetic

and particle radiations ) in the management ofpatients with cancer ( and other neoplasms ), alone,or combined with other modalities such as surgeryand chemotherapy


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The aim of radiation therapy

Is to deliver a precisely measured dose of radiation to a

defined tumor volume with minimal damage insurrounding healthy tissue , resulting in eradication ofthe tumor and high quality of life


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Goal :1.Radical radiation

Treatment intended to cure the patient of his or her disease. The dose is so high, involved tumor and any areas where

the risk of microscopic extension present.

2.Palliative radiation

Treatment intended to relieve the distressing symptoms of

advanced disease ( such as ;relief of pain, luminal patencyrestored, skeletal integrity preserve, organ functionreestablish,large mass, ulceration ). The dose given around2/3 of full dose and in a shorter time, more simpletechnique, and with minimal side effect.


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Technique of delivering dose1. External radiation

Radiation beams comes from outside of the body in thecertain distance

2. Brachytherapy

Introducing radioactive sources into body cavities (

intracavitary ) or inplanted into tissue ( interstitial )3. Internal radiation

Radioactives fluid introduced into the body orally orintravenously


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Steps in radiation therapy procedure

1. Clinical evaluation : pathobiology of tumor,diagnostic workup, staging

2. Therapeutic decision : goals ( cure or palliation ),

choice of therapy, modalities3. Tumor localization : primary tumor, regional,

sensitive organs )

4. Treatment planning ( simulation, computation, etc)

5. Treatment6. Periodic evaluation

7. Follow up


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Radiation dose

Radiation absorbed dose ( rad ) , the old one

Gy ( Grey ) equiv. with 100 cGy =100 rad , now usedroutinely


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Doses must be given in fractination, based on the

four Rs of radiobiology :1. Repair

2. Repopulation

3. Redistribution

4. Reoxygenation


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Various types of fractination Conventional dose : 200 cGy, 5 days a week

Hyperfractination : 115 cGy x 2/day, 5 days a week

Acceleration hyperfractination : 200 cGyx2/day

Split course : > 200 cGy/day


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Radiation given in three settings :

1. Where no other potentially curative treatment exist

2. Where alternative treatment is considered more

toxic3. When it can provide palliation in advanced disease

In some instances radiotherapy is the best approach


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External beam sources1. X-rays : - Superficial ( 80-150 KeV )

- Orthovoltage ( 250-300 KeV)

-Linear accelerator ( Linac ) ( 4-20 MeV )

2. Gamma rays : - Cobalt-60 ( 1.17, 1.33 MeV)

- Cesium-137 ( 0.66 MeV )

3. Particle electron : Linac


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Linac


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Direction of external beam

radiationsPlan parallel ( Right/left lateral )

Tangential/oblique ( medial/lateral )

Rotation


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Radioisotopes for brachytherapy Radium-226 ( 1.1 MeV)

Cesium-137 ( 0.66 MeV )

Cobalt-60 ( 1.17 MeV ) Iridium-191 ( 0.33-0.61 MeV )

Gold-198 ( 0.41-1.09 MeV )

Iodine-125 ( 0.025 MeV )


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Iridium - 192


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How to kill tumor cells by radiation Direct action

Radiation or photon energy directly damage the helicalchain of DNA

Indirect action

Radiation or photon energy react with

macromolecules /water---> free-radicals----> damagethe DNA


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The most common tumors treated

by radiation : Head and neck cancer ( nasopharyngeal, tonsils etc )

Uterine cervix carcinoma

Breast cancer Lung cancer

Basal cell carcinoma ( Basalioma )

Bone metastases


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Combination Therapy

Radiation and surgery

Indications :

1. Tumors with low cure rates by either surgery or radiation2. Anaplastic tumors with a great potential for vascular invasion

3. Tumors with a great potential for local or regional recurrence

4. Tumors with a great potential for residual disease after surgery

5. To preserve function6. To preserve cosmesis


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Rationale for preoperative

radiation Eradicate subclinical disease beyond the margins of

surgical resection

Influence cell viability

Sterilize limph node metastases outside operative field

Influence resectability

Decrease potential for dissemination

Example : Colorectal tumor


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Rationale for postoperative

radiation Treat known residual disease not resected

Destroy subclinical foci of tumor cells following thesurgery

Eradicate new disease in adjacent area ( includinglimph node )

Deliver higher radiation dosage to high-risk areas

Example : Breast cancer


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Combination of radiation with

chemo1. Neoadjuvant , to reduce initial tumor cell number before

definite surgery or radiation or both and potentially todecrease the viability of micrometastases

2. Adjuvant to eradicate micrometastases or tumor celldissemination outside the operated or irradiated volume

3. Concomittant chemo-irradiation

4. Definitive therapy, in tumor that are chemosensitive andcan be controlled with cytotoxic agents alone

5. Palliative therapy, in the treatment of syastemicmacrometastases or to relief symptoms in patients withchemosensitive tumors


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Some limitations of radiation

therapy Inadequate eradication of primary tumor

Regional microextensions or meta to the lymph nodeswhich may not be included

Clinically inapparent distant meta at the time of initialtherapy

Inaccurate tumor localization

Inadequate treatment planning Biologic tumor characterization that decrease the

effect of radiation


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Toxicity of radiotherapy Skin ( erythema, desquamation ) Mucous membrane ( mucocitis ) Hair ( alopecia )

Cornea ( keratitis ) Brain (tiredness,lethargy,nausea,vomiting, somnolent ,etc ) Lung ( pneumonitis, cough, dyspneu ) GI tract ( nausea, vomoting , diarrhea ) Bladder ( urinary frequency, dysuria ) Spinal cord ( neurologic defisit ) Liver ( hepatts ) Bone marrow ( suppression of WBC and platelets )


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Normal tissue tolerance doseWhole brain ( 50-55 Gy )

Spinal cord ( 44 Gy )

Brachial plexus ( 50 Gy )Whole lungs ( 20 Gy )

Part lung ( 40-50 Gy )

Pericardium ( 40 Gy )

Whole liver ( 20-30 Gy )

Thyroid gland ( 30 Gy )

Skin ( 55 Gy )


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Parotid gland ( 10 Gy, temporary dryness), 40 Gy(prolonged dryness )

Both kidney ( 20 Gy )

Ovary ( 2-6 Gy; permanent sterility )

Testis ( 3-4 Gy; permanent sterility )

Lens ( 5-10 Gy cataract formation )


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basic principles of radiation oncology

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