Abstract
Dosimetry in tissue exposed to the epithermal neutron beams utilized for BNCT is complex, due to the multiplicity of the possible neutron reactions and consequently of the secondary radiation that contains photons, charged particles and recoil nuclei. Owing to the different radiobiological effectiveness of the various components of the absorbed dose, it is necessary to attain the evaluation of each of them. In addition, the spatial distributions of these dose components changes considerably with size and shape of the irradiated volume. Therefore, BNCT dosimetry requires suitably developed calculations and experimental methods. In this work, Monte Carlo simulations in phantoms of different sizes and shapes have been developed. Experimental methods for separating the dose components, mainly based on gel dosimeters and thermoluminescence detectors, have been applied. Moreover, the change in the absorbed dose resulting from the addition of 157Gd was investigated. Both measurements and calculations have been done with the BNCT epithermal beam of the LVR-15 reactor.
Highlights
BNCT dosimetry is a challenging task, in the case of irradiations with epithermal neutrons, as required for deep tumor treatments
Dosimetry in tissue exposed to the epithermal neutron beams utilized for BNCT is complex, due to the multiplicity of the possible neutron reactions and of the secondary radiation that contains photons, charged particles and recoil nuclei
The epithermal neutrons are moderated mainly by the elastic scattering interactions with hydrogen nuclei 1H(n,n’)1H and the energy spectrum of BNCT neutron beams is suitably designed in order to get high fluence of thermal neutrons in a volume centered at a depth of about 2 cm
Summary
BNCT dosimetry is a challenging task, in the case of irradiations with epithermal neutrons, as required for deep tumor treatments. The dose contributions that have to be considered can be divided into three general groups, each characterized by a different spatial distribution: the dose coming from the charged particles generated by thermal neutron reactions with particular isotopes, the gamma dose (Dγ) and the dose due to epithermal- and fast-neutron elastic and anelastic collisions (Dfast). A significant percentage of the absorbed dose comes from gamma radiation, partially due to background (not considered in this work) and partially to the photons of 2.2 MeV emitted in the reactions of thermal neutrons with hydrogen (1H(n,γ)2H). This emission, in each point of the irradiated volume, is linearly correlated to the thermal. Owing to the high cross section (255000 b) of the reaction 157Gd(n,γ)158Gd, a considerable reduction of Φth and a noticeable increase of Dγ are expected
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