Boron Neutron Capture Therapy beam shaping assembly prototype MCNP and PHITS input files

BNCT BSA prototype

This release contains the simulation files of a BNCT BSA prototype which can be used to evaluate bulk moderating material at the CN accelerator facility at the INFN Legnaro National Laboratories. There are two simulation source files, MCNP contains the most updated version of the prototype, we recommend using this simulation geometry as an input also for PHITS. On the other hand PHITH source file contains a tetrahedral geometry which can be more easily manipulated for shielding evaluations, keep in mind that this source file misses the shielding polyethylene shielding around the lead reflector. Updated versions of the simulations files will be provided in future releases.

BSA prototype design

The goal was to design and build a prototype that embodied the key elements of the BSA created for clinical BNCT[1] in order to experimentally verify how well the BSA materials work together to moderate neutrons. As mentioned above, this structure is not intended to be a replica of the clinical BSA. Instead, it was intended to build a model of the BSA enabling the collection of data regarding the impact of various materials on the neutron spectrum and Monte Carlo validation.

Two configurations have been constructed, on the basis of their effectiveness in collimation and of the spectral modulation obtained by changing the moderator thickness. The first configuration (PHITS input files) consist of a 5 cm thick lead cylinder (reflector) with a cylindrical housing for the insertion of 5 cm diameter Alliflu elements. The length of the reflector is 25 cm. The reflector is surrounded by a 1 cm thick absorber of borated polyethylene. A collimator of borated polyethylene, 25 cm thick leaving a 5 cm diameter beam port ends the structure. The collimator is 25 cm long. The Alliflu elements can be housed in the core of the BSA prototype, inside the cylindrical reflector, allowing measurements with variable moderator thickness from 0 to 25 cm.

The second configuration (MCNP input files) consists in adding a shell made of polyethylene to configuration 1, with the aim of improving the moderation as well as the absorption of ambient radiation. The polyethylene additional shell in the second configuration was extended towards the target to better shield the neutrons emerging in all directions. This strategy plus the extra thickness of the absorber made it possible to reach a proton current of 6 μA in some of the measurements.

References

1. Postuma, Ian, et al. "A novel approach to design and evaluate BNCT neutron beams combining physical, radiobiological, and dosimetric figures of merit." Biology 10.3 (2021): 174.