BNCT dosimetry: peculiarities and methods

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

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

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 10B 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 3 mm, 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

LVR-15 reactor epithermal neutron beam parameters : results of measurements

The epithermal neutron beam of the LVR-15 reactor provides the appropriate conditions for varied BNCT activity. The principal parameters have been frequently determined. The following detectors have been used for the measurement: set of activation monitors of different nuclides irradiated in free beam and in the water phantom, Si semiconductor detector with 6LiF converter, twin ionization chambers, thermoluminescence dosimeters, gel dosimeters used for imaging of separate part of dose, neutron spectrometer of Bonner type. Obtained results of measured parameters are presented in the paper

LVR-15 Reactor Epithermal Neutron Beam parameters - results of measurements

The epithermal neutron beam of the LVR-15 reactor provides the appropriate conditions for varied BNCT activity. The principal parameters have been frequently determined. The following detectors has been used for the measurement: Set of activation monitors of different nuclides irradiated in free beam and in the water phantom, Si semiconductor detector with 6LiF converter, twin ionization chambers, thermoluminescence dosimeters, gel dosimeters used for imaging of separate part of dose, neutron spectrometer of Bonner type. Obtained results of measured parameters are presented in the paper

LHC RadMon SRAM Detectors Used at Different Voltages to Determine the Thermal Neutron to High Energy Hadron Fluence Ratio

The thermal neutron SEU cross-section of the Toshiba SRAM memory used in the LHC RadMon system was measured at different voltages. A method using the difference in its response compared to mixed particle energy field is proposed to be used as a discriminator between thermal neutron and high-energy hadron fluences. For test purposes, the proposed method was used at the CNGS and CERF facilities to estimate the field composition by counting SEUs at two different voltages and the results were compared to simulations

Methods for dose measurements in small phantoms irradiated at BNCT epithermal column

Suitable dosimeter methods have been proposed and tested,to measure the different dose contributions in small phantoms exposed to epithermal/thermal neutron beams designed for BNCT. One method is based on Fricke-gel dosimeter in small tubes of 2.8 mm of ex ternal diameter, that allow determining profiles of gamma dose and of boron dose.The other method is based on the use of TLD-700 chips, from whose answer the contribution of thermal neutrons is subtracted by means of appropriate parameters of the glow curve

Study of Epithermal-Neutron Spectrum Variation versus Depth in Water Phantoms

A study has been carried out concerning the energy spectrum of the epithermal beam designed for boron neutron capture therapy of the LVR-15 research reactor. Monte Carlo (MC) calculations concerning radiation transport and dose distribution in water volumes of various shapes exposed to the epithermal neutron beam were developed with MC N-Particle/MC N-Particle Extended calculations. In addition to the energy spectra at various depths in a water phantom, longitudinal and transversal profiles of the fluence of neutrons above and below the cadmium cutoff (0.5 eV) have been evaluated for different shapes of the phantom. In particular, significant differences were found in the spatial distribution of neutrons for energy E<0.5 eV. In order to confirm the reliability of simulations, a few depth profiles of neutron fluence below 0.5 eV, evaluated by means of MC calculations, have been compared with the profile of thermal neutrons obtained by means of experimental measurements. The consistency of results is good

Dose imaging in a thorax phantom with lung-equivalent volume at the epithermal neutron beam of LVR-15 reactor

A thorax phantom has been designed, consisting of PMMA and PE plates containing a cavity filled with a laboratory-made lung-substitute. Fricke-gel dosimeters have been placed in the lung-substitute volume, and the phantom has been irradiated at the epithermal column of LVR-15 reactor. Absorbed dose images have been obtained for both gamma radiation and charged particles emitted in the 10B reactions with thermal neutrons. Measurements with thermoluminescence dosimeters (TLDs) and Monte Carlo (MC) calculations have been performed too, in order to attain inter-comparison of results