Topology optimization design of the "Beam Shaping Assembly" of an AB-BNCT facility - application to the case of glioblastoma treatment.

This study aims to determine the optimal structure of the Beam Shaping Assembly (BSA) for an AB-BNCT (Accelerator-Based Boron Neutron Capture Therapy) facility. The aim is to maximize the possible depth of treatment for glioblastoma while ensuring that a treatment time constraint is not exceeded. Approach. To achieve this goal, we utilize a new optimization procedure known as topology optimization. This technique can accurately identify the most optimal structure of a nuclear device, in this case a BSA, to be identified among 9×101206 possible structures for the example given in this study. The exploration of such a vast space of configurations is inaccessible to any other method available to date. Main results. The topology optimization generated Air-AlF3-LiF-LiFPE BSA has an original structure that differs significantly from the structures previously tested by the BNCT community. This structure, which combines a ring collimator and a filter cone to mimic the effect of multi-field treatment, generates unprecedented treatment depths, with a Treatable Depth TD = 10.01 cm and an Advantage Depth AD = 12.48 cm (for 15 ppm of Boron-10 in blood, with a 3.5 tumor-to-blood Boron-10 concentration ratio), or TD = 10.30 cm and AD = 12.69 cm (for 18 ppm of Boron-10). These depths are much greater than any other design proposed to date by the community. The structure also verifies the latest proposed radiation protection constraints, which set limit values on its out-of-field leakages. Significance. The findings of this study indicate that topological optimization procedures are highly beneficial for the design of BSAs. In particular, the use of ring collimators could significantly improve the quality of BNCT treatments of brain tumors.