Quality assurance of computer controlled radiotherapy treatments

There is a need in conformal therapy, as in any radiation therapy, for adequate quality assurance of the treatment plan and the delivery of the treatment. This paper examines quality assurance of two methods of conformal treatment, on a cobalt treatment unit using computer control. Each of the two methods demonstrates a different aspect of computer controlled treatments. Following completion of each treatment plan, an additional "quality assurance plan" is prepared. This is used to assess the integrity of the treatment plan, and the precision with which the computer controls the treatment unit. A simple method, using solid state detectors in a Perspex phantom, is used to validate the dosimetry of the "quality assurance plan". Quality assurance of the computer control is performed daily prior to treatments. At each treatment, parameters identifying the start position and final position of the computer controlled couch movements and the exposure time are noted by the radiographers. Comparison of the recorded movement of the treatment couch and the exposure time with that intended during each course of treatment has demonstrated, inter alia, limitations on couch speed control at speeds of less than 10 mm per min.