The problem of radiotherapy treatment interruptions has been addressed taking into account the linear quadratic model. Simple treatment interruption recovery is possible by using the Biological Effective Dose equivalence between the initially planned total dose and the increased actual total dose. The supplement dose necessary to compensate for tissue proliferation during interruption, is to be considered. This is possible only for acute responding tissue with large alfa/beta ratio as tumors, epithelium, mucosa. However, a higher total dose planned for treatment interruption recovery may overcome late responding vascular and connective tissue or spinal cord tolerance where tissue proliferation is stimulated only after very long latent periods, well beyond the end of even prolonged treatments. Models of dose fractionation or hyperfractionation for recovery of tumor effect not exceeding the late responding tissue tolerance, can be devised by compromising between the planned and modified Biological Effective Dose both in acute and late response tissue.