Study of suitability of Fricke-gel-layer dosimeters for in-air measurements to characterise epithermal/thermal neutron beams for NCT

Abstract

The reliability of Fricke gel dosimeters in form of layers for measurements aimed at the characterization of epithermal neutron beams has been studied. By means of dosimeters of different isotopic composition (standard, containing (10)B or prepared with heavy water) placed against the collimator exit, the spatial distribution of gamma and fast neutron doses and of thermal neutron fluence are attained. In order to investigate the accuracy of the results obtained with in-air measurements, suitable MC simulations have been developed and experimental measurements have been performed utilizing Fricke gel dosimeters, thermoluminescence detectors and activation foils. The studies were related to the epithermal beam designed for BNCT irradiations at the research reactor LVR-15 (Řež). The results of calculation and measurements have revealed good consistency of gamma dose and fast neutron 2D distributions obtained with gel dosimeters in form of layers. In contrast, noticeable modification of thermal neutron fluence is caused by the neutron moderation produced by the dosimeter material. Fricke gel dosimeters in thin cylinders, with diameter not greater than 3mm, have proved to give good results for thermal neutron profiling. For greater accuracy of all results, a better knowledge of the dependence of gel dosimeter sensitivity on radiation LET is needed.

Feasibility study of optical imaging of the boron‐dose distribution by a liquid scintillator in a clinical boron neutron capture therapy field

“…Boron neutron capture therapy (BNCT) uses the nuclear reaction of 10 B(n, α) 7 Li, as expressed in Equation ( 1), to selectively kill tumor cells. 1 Following the reaction expressed in Equation ( 1), the excited state of the 7 Li nucleus ( 7 Li*) emits a prompt 478 keV gamma ray, as expressed in Equation (2). 10 B + n → { 7 Li + 𝛼 (6 %, Q = 2.79 MeV) 7 Li * + 𝛼 (94 %, Q = 2.31 MeV) (1) 7 Li * → 7 Li + 𝛾 (478 keV) (…”

“…1 Following the reaction expressed in Equation ( 1), the excited state of the 7 Li nucleus ( 7 Li*) emits a prompt 478 keV gamma ray, as expressed in Equation (2). 10 B + n → { 7 Li + 𝛼 (6 %, Q = 2.79 MeV) 7 Li * + 𝛼 (94 %, Q = 2.31 MeV) (1) 7 Li * → 7 Li + 𝛾 (478 keV) (…”

“…The physical dose deposited by 7 Li nuclei and alpha particles is known as the boron dose, and the treatment results of BNCT effectively depend on the boron dose. Hence, the direct measurement of boron-dose distribution is highly desirable for further progress in BNCT.…”

“…The detection of the 478 keV prompt gamma rays emitted from 7 Li*, as expressed in Equation (2), is a promising candidate technique that enables the direct evaluation of boron concentration or boron dose in patients, because the number of 478 keV prompt gamma rays is proportional to the number of boron neutron capture reactions. Thus, several studies have been conducted to realize this method.…”

Smart material based on boron crosslinked polymers with potential applications in cancer radiation therapy

“…In the last two years, scintillation detectors have been proposed for the discrimination of neutrons in mixed fields by means of adequate shielding and signal post-processing 37 . In medical physics, gel dosimeters doped with compounds based on B are used to mimic BNCT treatments and thus quantifying the neutron capture dose contribution 38 . Although many of these detection systems are capable of determining the neutron contribution, most of them still require signal post-processing and calculations in order to discriminate the neutron contribution to the total absorbed dose 39 , 40 .…”