Seventh lecture

Radiosensitivity & law of Bergonié and Tribondeau It is not clear why lack of differentiation of the cell results in radiosensitivity. It has been shown that undifferentiated cells or cells in the process of differentiation are easily killed by radiation. The length of time that cells remain in active proliferation relates to the number of divisions between the most immature stage and the final mature stage. The longer the cell remains in active proliferation, the greater its sensitivity to radiation.

Radiosensitivity & law of Bergonié and Tribondeau Bergonié and Tribondeau stated their law in1906 which is: “The radiosensitivity of a tissue is directly proportional to its reproductive capacity and inversely proportional to its degree of differentiation”

Radiosensitivity & law of Bergonié and Tribondeau Since the time that the law of Bergonie and Tribondeau was formulated, it is generally accepted that cells tend to be radiosensitive if they : i-have a high division rate. ii-have a high metabolic rate. iii-are of a non-specialized type. iv-are well nourished.

Radiosensitivity & law of Bergonié and Tribondeau The law can be used to classify the following tissues as radiosensitive: i-germinal cells of the ovary and testis. ii-Haematopoietic tissues: red bone marrow, spleen, lymph nodes and thymus. iii-Epithelium of the skin. iv-Epithelium of the GIT.

Radiosensitivity & law of Bergonié and Tribondeau The law can be used to classify the following tissues as radioresistant: i-Bone ii-Liver iii-Kidney iv-Cartilage v-Muscle vi-Nervous S.

Stochastic effects of radiation Are those in which the probability within a population of the effect occurring increases with dose without threshold Any dose, therefore, has a certain probability, however low, of causing the effect. Stochastic effects may result from injury to a single cell or a small number of cells. Carcinogenic (cancer) and genetic effects are examples of stochastic effects.

Non-stochastic effects of radiation Non-stochastic, or deterministic, effects are those in which the severity of the effect varies with the dose. A threshold dose may exist. Are considered to result from the collective injury of a substantial number of cells. Example of such effects are cataracts, skin ulcerations or burn, depletion of blood- forming cells & impairment of fertility