Physics and Principles of Radiotherapy Cancer is a

• Physics and Principles of Radiotherapy • • Cancer is a group of cells growing in an uncontrollable manner and is capable of spread to distant organs. • • Basis of Radiotherapy: - Radiation damages the DNA and therefore stops cell division.

• Types of Radiation in Use • Electromagnetic. Radiation [Photons]X-rays } • Gamma Rays • Beta Rays • All cause ionizations and energy transfer

• ABSORPTION OF RADIATION: Methods of energy transfer to matters • [a] Photoelectric Effect • [b] Compton Interaction • [c] Pair Production

• BIOLOGICAL EFFECTS OF RADIATION • 1. Indirect Action – Damage to DNA by free radicals produced by interaction of radiations with water molecules in tissue. • • • Radiation H 20+ + ee- + H 20 H 20+ H+ + OH. H 20 H. + O HH. & OH. [Primary radicals] RH + OH. R’ + H 20 RH + H. R. + H 2 R. [Secondary free radicals]

• • • Direct Action Radiation RH R. + H. [organic molecule] [free radicals] R. + 02 R. 02 [Organic peroxide radical] H. + 02 H 02. 2 H 02 H 202 + 02 Peroxide radicals are biologically damaging Oxygen Effect – Increased biological damage in the presence of oxygen.

• • • Other forms of Radiation Enhancement [a] Type of radiation [High LET radiation] [b] Drugs e. g. misonidazole [c] Hyperthermia [d] Fractionation [e] Continuous low dose radiation

• FORMS OF APPLICATION OF RADIOTHERAPY • 1 [a] Superficial (100 - 150 v) [b] Teletherapy [Megavoltage]- Cobalt 60 and Linear Accelerator • 2 Brachytherapy [short Therapy] using radioactive sources • - Moulds • - Implants • - Intracavitary therapy

Pre- Radiotherapy Assessment a. Clinical Exam and Staging and Lab Investigations b. Review of Histopathology - Grade • - Lymphatic/Blood vessel invasion • - Completeness of excision • - Multifocality the Multicentricity c. Operation Findings and localization of residual disease d. Chest radiograph e. Liver the Bone Scans etc.

PRINCIPLES OF APPLICATION a. Preoperative – reduce blood spread - render operable b. Postoperative – prophylactic treatment - for residual disease c. Sole treatment for inoperable tumours d. Palliation – pain, pressure, bleeding, pathological fractures

• • • SIDE EFFECTS OF RADIATION THERAPY Nausea and vomiting Diarrhoea Anaemia Growth Retardation Sterility Radiation Syndromes – Total body irradiation dose [Gray] Dose Time of death Mode 2 - 10 Gray 10 -30 days Bone marrow syndrome 10 -100 Gray 3 -5 days GIT Syndrome > 100 Gray few minute-48 hrs CNS syndrome [irreversible] Effect also on Gonads, Eyes, skin, lymphocytes

USE OF UNSEALED RADIOSOTOPES FOR MALIGNANT AND BENIGN DISEASES • Properties Required 1. Non- toxic 2. Preferentially absorbed by organs being investigated or treated. 3. High specific activity 4. Sufficient long biological half-life 5. Must be pure B-emitter.

• • CONTRAINDICATIONS - Patients of childbearing age - Children - Pregnant women

EXAMPLES OF DISEASES • • • Thyrotoxicosis. } Use of radioactive iodine. Thyroid carcinoma } Polycythaemia Vera Rubra- P 32 Bone metastases – radioactive strontium