Radiation Biology for Physical Scientists/Radiation Sensitivity of Cells

Interaction of Radiation with Matter Radiation Induced Damage and Repair The sensitivity of cells to radiation depends on cell cycle phase, level of differentiation, metabolic rate and rate of division. thumb|Basic events in the cell cycle courtesy of Kelvinsong Based on Cell Cycle Cells propagate through division through a series of events. Radiation resistance through the cell cyle correlates with the level of sulfhydryls which are natural radiation protectors.Cells are most sensitive in the M phase and often G2. Slow cycling cells are resistant in early G1 and sensitive in late G1. Cell resistance is greatest in the last S phase because of the effective repair through homologous recombination. Based on Function The Law of Bergonié and Tribondeau states cells that are dividing quickly, have less specialized functions and high metabolic rate are sensitive to radiation. Less Resistant Spermatogonia Epidermal Stem Cells Osteoblasts Spermatozoa More Resistant Nerve Cells The difference in radiation sensitivity of tissues is based on the differences in the level of specialization and proliferation inherent in their critical cells. Acute Responding Tissues Late Responding Tissues Gut Brain Skin Spinal Cord Bone Marrow Kidney Mucosa Lung One exception to the law are T-lymphocyte cells which are sensitive to radiation and highly differentiated. Classification of cell radiation sensitivity has also been done based on histologic observation of cell death (Casarett's Classification) and reproductive kinetics (Michalowski's Classification). References Hall, Eric and Giaccia, Amato. Radiation Biology for the Radiologists. Lippincott Williams & Wilkins, 2006.