ABSTRACT
Low dose-rate irradiation is the ultimate form of fractionation, equivalent to multiple infinitely small fractions being given without radiation-free intervals, and thereby damage induction and repair take place at the same time. In clinical radiotherapy, continuous low dose-rate (CLDR) is widely used in brachytherapy either by permanent or temporary implantation of radioactive sources (e.g. 125I, 103Pd) into tumours. By utilizing remote afterloading of medium or high dose-rate sources, notably 192Ir, various combinations of dose-rate and fractionation can also be chosen, such as pulsed dose-rate (PDR) and high doserate (HDR) brachytherapy. With external-beam treatments using intensity-modulated radiotherapy (IMRT), the dose-rate effect may also have some impact as the longer treatment times per session, which can be needed in more complex plans, may lead to a reduction in effectiveness.
