Principles of Clinical Radiation Oncology
Radiotherapy is the therapeutic use of high-energy ionizing radiation. These are either electromagnetic waves consisting of X-rays and gamma rays, or subatomic particles such as B particles, high-energy electrons, and neutrons. Ionizing radiation penetrates tissues to different depths according to its type of energy and physical nature. The free radicals produced by ionizing radiation react with a wide variety of essential macromolecules within the cells. The important reactions, however, are those that occur with DNA (Fig. 1). Because of the unique function of many parts of this molecule, DNA damage with loss of integrity leads to cell death or muta-genesis. By damaging DNA, radiation interferes with cell division. This process is unselective; it occurs both in cells of normal tissues and in those of tumors. The therapeutic usefulness of radiotherapy, therefore, depends on the differential sensitivity of some tumors to irradiation, on careful treatment planning and dose prescription to minimize normal tissue damage, and on the patient’s tolerance to radiation damage to parts of some organs. Radiotherapy treatment planning is an important part of the radiation oncologist’s work.
KeywordsTherapeutic Ratio Skin Erythema Therapeutic Gain Recoil Electron Gentian Violet
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