High dose rate gynecological applications--radiobiological considerations based on the alpha-beta model

We compare the relative efficacy of high dose rate (HDR) and low dose rate (LDR) irradiation in gynecological implants, using formulations based on the linear-quadratic (alpha-beta) model. We consider both acute reaction and late effect as endpoints in evaluating equivalence for HDR and LDR treatments, at Point A (as defined in the text) and at other locations. We define a therapeutic factor gamma as an index for relative efficacy, with gamma > 1 indicating a gain in substituting HDR for LDR. It is found that gamma < 1 for most clinical situations, although a modest decrease (of about 15%) in dose to critical organs for HDR would raise gamma above unity.