Radiotherapy dose enhancement using BNCT in conventional LINACs high-energy treatment: Simulation and experiment

Abstract

Aim

To employ the thermal neutron background that affects the patient during a traditional high-energy radiotherapy treatment for BNCT (Boron Neutron Capture Therapy) in order to enhance radiotherapy effectiveness.

Background

Conventional high-energy (15–25[[ce:hsp sp="0.25"/]]MV) linear accelerators (LINACs) for radiotherapy produce fast secondary neutrons in the gantry with a mean energy of about 1[[ce:hsp sp="0.25"/]]MeV due to (γ, n) reaction. This neutron flux, isotropically distributed, is considered as an unavoidable undesired dose during the treatment. Considering the moderating effect of human body, a thermal neutron fluence is localized in the tumour area: this neutron background could be employed for BNCT by previously administering ¹⁰B-Phenyl-Alanine (¹⁰BPA) to the patient.

Materials and methods

Monte Carlo simulations (MCNP4B-GN code) were performed to estimate the total amount of neutrons outside and inside human body during a traditional X-ray radiotherapy treatment.

Moreover, a simplified tissue equivalent anthropomorphic phantom was used together with bubble detectors for thermal and fast neutron to evaluate the moderation effect of human body.

Results

Simulation and experimental results confirm the thermal neutron background during radiotherapy of 1.55E07[[ce:hsp sp="0.25"/]]cm⁻²[[ce:hsp sp="0.25"/]]Gy⁻¹.

The BNCT equivalent dose delivered at 4[[ce:hsp sp="0.25"/]]cm depth in phantom is 1.5[[ce:hsp sp="0.25"/]]mGy-eq/Gy, that is about 3[[ce:hsp sp="0.25"/]]Gy-eq (4% of X-rays dose) for a 70[[ce:hsp sp="0.25"/]]Gy IMRT treatment.

Conclusions

The thermal neutron component during a traditional high-energy radiotherapy treatment could produce a localized BNCT effect, with a localized therapeutic dose enhancement, corresponding to 4% or more of photon dose, following tumour characteristics. This BNCT additional dose could thus improve radiotherapy, acting as a localized radio-sensitizer.