Boron neutron capture enhancement study for radiation therapy with fast fission neutrons

While the number of centers offering fast neutron therapy (FNT) for cancer treatment has declined, boron neutron capture therapy (BNCT) experiences a revival. In contrast to the remaining FNT facilities actively treating patients using accelerator-based fast neutron sources, the fission neutron therapy facility MEDAPP at the research reactor FRM II in Garching was used in the past for patient treatment with fast fission neutrons. In the presented paper, we investigate the enhancement of the dose deposition by boron neutron capture reactions in fission-based fast neutron therapy driven by the motivation to explore the feasibility of an advanced treatment option. Here, the main focus is on the investigation of the combination of the fission neutron spectrum used for radiotherapy in the past with the B-10 concentration that are required for BNCT. In addition, a higher B-10 concentration and a modified neutron spectrum with a high thermal component are investigated. Including a higher B-10 concentration is driven by the ongoing research in the development of B-10 delivery agents. The study was performed using Monte Carlo simulations to calculate the dose rates in a water phantom and B-10 enriched regions of interest in different locations close to the surface of the water phantom. The influence of the B-10 concentration on the dose rate was less than 3% for all locations of the enriched regions for the combination of the clinical FNT spectrum and the clinical B-10 concentration. The dose rate is highly increased by the thermal component of the neutron input spectrum. While the dose rate enhancement is low for the combination of clinically available FNT and BNCT treatment scenarios, a potential biological selectivity of the neutron capture reactions is not represented in the physical dose rate. Further evaluation of the latter scenario and the exploitation of the thermal component within the modified spectrum appears promising.