R5.1: Variations In Cellular Radiation Sensitivity

Cell Structures and Radiosensitivity

The various parts of the cell have different sensitivity to radiation. This has been shown by localised alpha-irradiation of cell structures. Alpha particles have such short range that selective irradiation of cellular components is possible.
Overall, the nucleus is the most sensitive part of the cell, due to the presence of DNA. This is the target of ionising radiation in radiotherapy. The cell membrane and cytoplasm are relatively resistant.

Cell Cycle and Radiosensitivity

By synchronising the cell cycle in a population of cells (possible through physical or biological means) it is possible to examine the effects of radiation on different parts of the cell cycle. Studies of this nature have shown:

  • Cells in late G2 and M phase are the most sensitive
  • Cells in S phase, and particularly late S phase, are more resistant
  • Cells in G1 phase have an average sensitivity