Beta Enhancers: towards a local dose enhancer device for Boron Neutron Capture Therapy (BNCT) on superficial tumors

Abstract

BNCT is a cancerous cells selective, nonconventional radiotherapy modality to treat malignant tumors such as glioblastoma, melanoma and recurrent head and neck cancer. It consists of a two-step procedure: first, the patient is injected with a tumor localizing drug containing a nonradioactive isotope (Boron-10) with high slow neutron capture cross-section. Secondly, the patient is irradiated with neutrons, which are absorbed by the Boron-10 agent with the subsequently nuclear reaction B-10(n,a)Li-7, thereby resulting in dose at cellular level due to the high-LET particles. The Argentine clinical facility for superficial tumors treatment is located at the RA-6 Research Reactor (Bariloche Atomic Center). Due to the beam penetration, the total absorbed dose in the first few millimeters of tissue is lower than in the maximum flux. Thus, the introduction of a suitable device over the irradiated area is considered to allow a local dose increase by means of high energy Beta particles emission, without substantially perturbing the primary in-depth dose profile. These devices are called Beta Enhancers (BE) and were studied by Monte Carlo transport code modeling, experimental measurements and retrospective treatment planning evaluation of selected nodular melanoma treatments of the Argentine BNCT patients. Pre-clinical studies were carried out in a nude mice cancer model for BNCT at the RA-6 facility, in order to preliminarily assess toxicity and efficacy of BE in-vivo implementation. Nude mice were separated into five groups of 5-9 animals each: control group, NCT (without boron agent) irradiation, NCT+BE irradiation, BNCT irradiation and BNCT+BE irradiation. The results demonstrate the technique efficacy, highlighted between NCT and NCT+BE groups. There was no toxicity evidence.