Monte Carlo benchmark of the experimental evaluation of the activation processes in an electron linear accelerator for radiotherapy applications

Several kinds of isotopes are generated during radiotherapy treatments with high-energy electron sources due to the onset of many nuclear reactions. These isotopes are often unstable, can appear both in the device and in the treatment chamber materials and, as a consequence of the decay process, involving also gamma-ray emissions, some additional dose is given to the patient and to the radiotherapy unit staff. These effects have been experimentally monitored with a LaBr detector for gamma spectrometry. Then the measurement setup and data have been benchmarked through Monte Carlo (MC) simulations, with the MCNPX code, aiming to evaluate all kinds of activation, due to both photons and photoneutrons. All the MC activation estimates have been parameterized with respect to the 187W produced in the primary collimator of the accelerator. The simulation results obtained with MCNPX have shown a good agreement with the experimental measurements. The results suggest a possible general approach to perform the activation analysis by coupling the experimental spectrometric measurements with MC calculations to properly identify photopeaks and source components.