Radiotherapy
is the use of x-rays and similar rays (such as electrons) to treat disease Radiotherapy involves the exposure of parts of the body to radiation, beams of high-energy X-rays, gamma rays or particles. The purpose is to destroy cells such as cancer cells that grow abnormally rapidly and in abnormal sites. The doctor who carries out the treatment is called a radiotherapistRadiotherapy
Energy & penetrating power of ionizing radiation increase as photon wave length Super voltage radiation >500 Kv Ortho voltage radiation 140-500 Kv superficial radiation 10-50 KvRadiotherapy
Super voltage radiation over 500 kilovolts (Kv) Reduced absorption in bone Less damage to skin at the portal entry Reduced lateral scatter of radiation into other tissueRadiotherapy
Orthovoltage & the use of superficial mechanics may yield an advantage in treatment of skin or other superficial tumour In a given dose to the soft tissue of the oral cavity the osteocytes and vascular structure of the mandible absorb much less from super voltage than from orthovoltage
Radiotherapy
external radiotherapy internal radiotherapyExternal radiotherapy
is normally given as a series of short, daily treatments in the radiotherapy department, using equipment similar to a large x-ray machine The treatments are usually given from Monday to Friday Each treatment is called a fraction. Giving the treatment in fractions ensures that less damage is done to normal cells than to cancer cells. The damage to normal cells is mainly temporary, but is the reason why radiotherapy has some side effectsInternal radiotherapy
by putting solid radioactive material (the source) close to or inside the tumour for a limited period of time by using a radioactive liquid, which is given either as a drink or as an injection into a veinRadiation according to application
Intracavitery irradiation Hollow container with radioactive isotpes Sinus (antrum) & nasal cavity tumour Interstatial radiation Inserted directly into the tumour Radium, cobalt-60, radio active gold Carcinoma of the tongue, tonsil, oral cavity, metastatic neck lymph nodesTreatment planning in radiotherapy
Guide lines for anatomic localization of tumour Tomography, CT scan, MRI, xerography, contrast radiography Reproducibility of daily treatments To ensure accuracy of delivery of radiation to the tumour Immobilization devices such as head straps & bite blocksRadiotherapy
Radio curability: a tumour is cured by maximal tolerable dose of radiation Radioresponsive: refer to regression after radiation but not to whether a tumour is radiocurable Radiologic definition of death is in ability to reproduceCell cycle effect
The lethal effects of radiation are cell cycle specific Cells are generally more sensitive near or at mitosis If G1 (pre DNA synthetic gap) is appreciable in length a resistant period is seen early followed by a decline in survival toward S (the phase of DNA synthesis) The end of G1 may be as sensitive as M (mitosis )