MEDRADSC 3U03 Lecture Notes - Lecture 4: Histopathology, Late Effect, Grey Matter
4 Jan 2017
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Document Summary
Cells of normal tissues are not independent, but are integrated to form a complete structure. There is a delicate balance between cell birth and death: to maintain cell number, to maintain tissue organization/integrity. The limiting factor on radiation therapy is the response of normal tissue. Inherent cellular radiosensitivity: tissue kinetics, organization of cells in the tissue. The majority of effects of radiation on normal tissue is attributed to the depletion of a cell population by cell killing. However, some side effects cannot be explained by killing: nausea/vomiting a few hours after abdominal irradiation, fatigue following large volume irradiation, somnolence following cranial irradiation, acute edema/erythema resulting from radiation-induced acute inflammation and associated vascular leakage. These effects are most likely mediated by inflammatory cytokines. With individual cells there is a monotonic relationship between dose and cell killing. Not so with tissue: no effects are seen with small doses. Increasing severity of effects are seen with increasing dose above a threshold level.
