Preliminary Monte Carlo study of CZT response to BNCT (n+γ) background

Boron Neutron Capture Therapy (BNCT) effectiveness depends on the therapeutic dose delivered in tumour when targeted by a sufficient amount of 10B atoms and exposed to a proper flux of thermal neutrons. Presently these quantities are measured indirectly. The availability of an in vivo and real time dose monitoring tool would be a tremendous achievement to fully exploit BNCT. To this end, a Single-Photon Emission Computed Tomography (SPECT) can measure the 478 keV γ-ray emitted after 94% of 10B capture reactions. Presently, the Italian National Institute of Nuclear Physics (INFN) is supporting the 3CaTS project whose aim is to develop a dedicated BNCT-SPECT based on CdZnTe (CZT) semiconductor detectors. A BNCT-SPECT must operate in a highly intense (n + γ) radiation field. Thus, it is important to study the response of CZT detectors when working in such challenging conditions. In the present work we focused on three main aspects: i) the spectra of the radiation background expected in an accelerator-based BNCT treatment room; ii) the interaction of the thermal neutrons with cadmium present in the crystal; iii) the estimation of the recorded photon counts spectrum when a 478 keV photon source is simulated inside a tissue equivalent phantom.