Guidelines for Complications of Cancer Treatment Vol VIII Part B

traversed by a charged particle but are in close proximity tocells that are bombarded by the charged particle (6).Tumor Types: Radiation is known to induce both leukaemiaand solid tumor. Latent period for secondary leukaemia isusually shorter (around 5 years) while for solid tumor, themedian is around 10 years. Amongst solid tumors it can causeboth sarcomas and carcinomas. Sarcomas can be in soft tissueor bone; common types are osteosarcoma, fibrosarcoma,malignant fibrous histiocytoma, angiosarcoma andchondrosarcoma. Incidence of radiation associated sarcomais reported to be 0.03- 0.25% of all patients receivingtherapeutic irradiation. In some cases radiation carcinogenicityis modified by life-style (e.g. higher incidence of lung canceramong survivors of Hodgkin’s lymphoma with smoking) orby genetic influence (e.g. higher incidence of osteosarcomain patients with hereditary retinoblastoma and germ linemutation of RB gene).Dose-Risk Relationship: Relationship between radiation doseand cancer risk comes from studies of Japanese atomic bombsurvivors, individuals with occupational radiation exposure,diagnostic radiology and use of RT for management of nonmalignantdiseases. For most solid tumor there is a linearrelationship up to 5 Gy and for leukaemia linear increase inrisk up to 1.5-2 Gy. These observations have led to the beliefthat risk of RAM is higher in the tissues exposed tointermediate doses, while tissue exposed to lethal doses in therange of >30 Gy, radiation is often lethal and does not inducecarcinogenesis. There is also variation in the sensitivity ofdifferent organs with regards to cancer induction by radiationwith sites such as thyroid, breast and bone marrow being moresensitive.Impact of newer radiation technology: Rapid advancementsin technology have ushered in the era of high-precisionradiotherapy such as three-dimensional conformal radiation284