Radiation Biology for Physical Scientists/Radiation Sensitivity of Cells

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.