MEDRADSC 3U03 Lecture Notes - Lecture 7: Absorbed Dose, Equivalent Dose, Radiosensitivity

• School: McMaster University
• Department: Medical Radiation Sciences
• Course: MEDRADSC 3U03
• Professor: Cathy Hayward

Document Summary

There is a dramatic dose-rate effect: repair of sub-lethal damage. As dose rate becomes very low cell division begins to dominate: exposure time is longer than the cell cycle, at very low dose rates there is minimal net cell killing for even very large doses. Too long a between fractions: tumour cells can begin to proliferate, accelerated repopulation. Fi(cid:396)st 0. 6gy of ea(cid:272)h day"s fraction needed to overcome proliferation from previous day. Too short a period between fractions: particular importance in hyperfractionation regimes. In vitro time of repair is 1hr. Incidence of late effects worsen for inter-fraction intervals of less than 4 hours. Equal doses of different types of radiation do. Lecture 7 (2) not produce equal biologic effects: 1gy neutrons produces a greater effect than 1gy x-rays, key lies in the pattern of energy deposition at the microscopic level (let) (cid:862)the rbe of some test radiation (r) compared with x-rays is defined as the ratio.