Fluorescent Neutron Track Detectors for Boron-10 Micro-Distribution Measurement in BNCT: a Feasibility Study

The interest in Boron Neutron Capture Therapy (BNCT) has been recently increasing thanks to the latest advancements in accelerator technology which allow to generate the required neutron field from accelerator facilities that could be hosted in hospitals or clinical centres. BNCT is a form of radiation therapy which relies on the highly localised and enhanced biological effects of the boron-10 (B-10) neutron capture (BNC) reaction products to selectively kill cancer cells. The BNC products are low-energy alpha and lithium ions, which are characterised by a high Linear Energy Transfer (LET) and a very short range lower than 9?m. The energy deposition and interaction with critical biological target such as DNA molecules is therefore strongly dependent on the B-10 spatial micro-distribution into the cells. In this framework, the Fluorescent Nuclear Track Detectors (FNTD) could be a promising device for the visualisation of the ion traversals induced in BNCT. FNTD consists of a fluorescent single-crystal aluminium oxide doped with carbon and magnesium, coupled with a Confocal Laser Scanning Microscopy (CLSM) read-out. Its biocompatibility allows to deposit and grow cells samples on its surface. If a layer of borated cells is deposited and irradiated by a neutron field, the energy deposited by the BNC products and their trajectories can be measured by analysing the corresponding track spots induced at different depths of the detector. This allows to reconstruct the position where the measured particles were generated, hence the micro-distribution of B-10. A FNTD was tested in three irradiation conditions to study the feasibility of FNTD for BNCT applications. The device was firstly irradiated by the alpha particles emitted by an Am-241 source (with energy of about 5.5 MeV). The same radiation field moderated by a 23?m layer of Mylar was then used to obtain alpha particles with a lower energy of about 2.5 MeV, thus closer to BNC products. Finally, the FNTD was tested at the University of Pavia’s LENA (Applied Nuclear Energy Laboratory) under a thermal neutron beam. A standard reference material (SRM) consisting of boron implanted on a silicon wafer was placed on the detector surface to reproduce a typical BNCT radiation field. The FNTD allowed to successfully measure the correct alpha particles range and mean penetration depth expected for all the radiation fields employed. This work proved the feasibility of FNTD to reconstruct the tracks of the alpha particles produced in typical BNCT conditions. Hence, FNTD will allow to measure the intra-cellular micro-distribution of B-10, bringing a significant contribution to the advancement of BNCT research. With this purpose, further experiments at LENA irradiating borated cell samples are planned.