Seventh lecture Radiosensitivity law of Bergoni and Tribondeau

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 in 1906 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 iv-Cartilage v-Muscle iii-Kidney 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 bloodforming cells & impairment of fertility