Induced radioactive potential for a medical accelerator.

Medical accelerators operating over 10 MV can induce short-lived radionuclides in components near the beam and in the air (McGinley 1992). We evaluated a Clinac 2100 C/D at 18 MV photon mode for radionuclidic exposure, contamination, and airborne potential to the accelerator staff entering the room after patient radiation treatment. The gantry, patient couch, wedges, floor, and air were activated. Most activated components appear to decay with a half-life of 2.5 min, except the gantry and port with half-lives approaching 10 min. The highest exposure was from the port at <2 mR h(-1). No removable contamination on any activated component was detected including coolant water in the machine. Airborne radionuclides were measured in the room and at the roof exhaust. The airborne potential is short lived because of ventilation and decay with the highest exposure of 0.3 mR h(-1) lasting for 1 s. Our measurements support the insignificant exposures received by accelerator staff wearing whole body personnel monitors. Accelerator roof effluents to unrestricted areas during patient treatments indicate that regulatory limits are not exceeded.