Determination of absorbed dose in a patient irradiated by beams of x or gamma rays in radiotherapy procedures

Several important changes in the underlying physical concepts of radiotherapy are discussed. Radiotherapy with external photon beams is now carried out to a very large extent with radiation of high energy. However, medium and low energy photons still have a place and give rise to problems to which special attention has to be drawn. This report will assume the use of high energy radiation (including 60Co gamma rays) unless otherwise stated. Isocentric techniques are now fairly common and the dosimetric procedures used with these techniques are somewhat different from those used with the more traditional techniques based on a fixed source-skin distance (SSD). The digital computer is widely and increasingly used as a means of calculating dose distributions and for other procedures discussed in this report