A study of the protection against induced radioactivity from Varian Clinac 21EX accelerator

Objective: To measure and analyze Varian Clinac 21EX accelerator induced radioactivity, and to provide specific recommendations and ways of radiation protection for radiotherapy technicians. Methods: To simulate the working environment of radiotherapy technician, and to detect induced radioactivity variation of Varian Clinac 21EX accelerator that induced by 15 MV X-rays under different conditions of beam field area, dose, time, distance and by high energy electron beam (12, 16, 20 MeV) at the different time. Results: The induced radioactivity level was not influenced by different beam field area, and was increased with increasing dose(r = 0.930, P < 0.05), decreased with time increase (r = -0.84, P < 0.05), decreased with distance increase (r = -0.975, P < 0.05). The induced radioactivity attenuation levels of the different doses at the same time are different, and have the common characteristic that the induced radioactivity attenuation rate is faster in the initial times. The induced radioactivity levels of high energy electron beams were significantly lower than those of high-energy X-rays. Conclusions: During radiotherapy positioning, it is necessary to take measures to protect against the induced radioactivity when high-energy rays with energy greater than 10 MeV will be used. The radiotherapy technician should take the different time and energy interval steps for the different ray type and energy and dose in order to meet the radiation protection principle of optimization. (authors)