Volume effects in radiobiology as applied to radiotherapy

Purpose: To explore the radiobiological evidence for a dependence of normal tissue complication probability on irradiated normal tissue volume. Materials and methods: Data from experimental studies on the volume effect in different organs, using different criteria of structural or functional o rgan damage and in different animals, were evaluated to investigate the vol ume effects for structural radiation damage as opposed to functional radiat ion damage, and the importance of organ anatomy and dose distribution withi n the organ on the development of chronic radiation damage in the respectiv e organ. Results: There is little or no volume effect for structural radiation damag e, however, some very pronounced volume effects have been reported for func tional damage. Volume, as such, is not the relevant criterion, since critic al, radiosensitive structures are not homogeneously distributed within orga ns. Conclusion: Volume effects in patients and experimental animals are more re lated to organ anatomy and organ physiology than to cellular radiobiology. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.