<prompt> Which is not the R of RadiobiologyRepairRedistributionRepopulationReperfusion  <response>: The Four Rs of Radiobiology Four major factors are believed to affect tissues response to fractionated radiation: Repair of sublethal damage to cells between fractions caused by radiation Repopulation or regrowth of cells between fractions Redistribution of cells into radiosensitive phases of cell cycle Reoxygenation of hypoxic cells to make them more sensitive to radiation 