How Low Can You Go? The Radiobiology of Hypofractionation

Hypofractionated radical radiotherapy is now an accepted standard of care for tumour sites such as prostate and breast cancer. Much research effort is being directed towards more profoundly hypofractionated (ultrahypofractionated) schedules, with some reaching UK standard of care (e.g. adjuvant breast). Hypo fractionation exerts varying influences on each of the major clinical end points of radiotherapy studies: acute toxicity, late toxicity and local control. This review will discuss these effects from the viewpoint of the traditional 5 Rs of radiobiology, before considering non-canonical radiobiological effects that may be relevant to ultrahypofractionated radiotherapy. The principles outlined here may assist the reader in their interpretation of the wealth of clinical data presented in the tumour site-specific articles in this special issue. (C) 2022 The Authors. Published by Elsevier Ltd on behalf of The Royal College of Radiologists.

Automated summary

Hypofractionated radical radiotherapy has become the standard of care for tumors like prostate and breast cancer, and there are more profoundly hypofractionated (ultrahypofractionated) schedules being explored. The effects of hypo fractionation on acute toxicity, late toxicity, and local control in radiotherapy studies vary. This review discusses these effects from the perspective of traditional radiobiological principles and considers non-canonical radiobiological effects that may be relevant to ultrahypofractionated radiotherapy.