On the neutron radiation field and air activation around a medical electron linac.

In high-energy photon therapy, several radiation protection issues result from photonuclear reactions. In this study, the photoneutron radiation field around a Varian Clinac linear accelerator in 18 MV-X mode within two different radiotherapy bunkers was investigated by means of Monte Carlo simulations using the FLUKA code as well as ambient dose-equivalent measurements. Furthermore, the activation of the air inside the treatment room due to photonuclear reactions (13N and 15O) and the capture of photoneutrons moderated down within the bunker (41Ar) was studied by FLUKA simulations. From the simulation results, the annual effective dose to medical workers due to photoneutrons and activated air was estimated. The emission of radioactivity due to ventilation of the treatment room was found to be negligible.