Photoneutron source for in-hospital BNCT treatment: PSIHO

The photoneutron source in-hospital project (PSIHO) ongoing within the Italian Institute for Nuclear Physics (INFN) makes use of the linear high-energy electron accelerators (18–25 MV) already available in hospital radiology units as a source of neutrons, after having fitted a neutron photoconverter. The goal of the project is to optimize neutron photoproduction by using a suitable photoneutron converter consisting in a high-Z core for neutron production surrounded by low-Z material for the moderation of initially high-energy neutrons down to thermal or epithermal energies. This device is a passive shield which does not entail any modifications to the accelerator and can be easily installed and removed from the accelerator head. Different kinds of optimized moderating structures can be produced for thermal, epithermal or mixed neutron beams, depending on the medical requirements.

In-hospital photoneutron radiotherapy extends the possibilities of boron neutron capture therapy (BNCT) to external treatment of diffused tumors when other methods are not possible or inadequate. By proper material and geometry optimization, interesting flow-rates of thermalized neutrons can be made available, with minimized fast neutron and gamma backgrounds, for a fractionated type of BNCT devoted to external treatment of some specific tumors. In the future, photoneutron converters made of high-Z materials, shaped to produce a thermal beam inside an irradiation cavity and easy to install or remove could become a common supplement to radiotherapy treatment. Several prototypes have been built, following feasibility studies on beam-shaping assembly using MCNP-GN and Geant-4 simulation codes, and these prototypes have been tested in various hospitals equipped with high-energy linear accelerator facilities.