EURADOS Working Group 6, Computational Dosimetry, a history of promoting good practice via intercomparisons and training

This paper is the editorial of a special issue of Radiation Measurements on EURADOS intercomparisons in computational dosimetry. The articles in this special issue cover complex problems in terms of geometry, particle types, energy ranges, coupled calculations and also scale, with the possibility of performing Monte Carlo calculations on micro and nano dosimetric scales now feasible. A summary of the exercises is provided in the first article of the Special Issue, which presents the findings and common conclusions from the ten articles reporting the results of the different exercises. One of these issues was the correct assessment of bone marrow dose, which prompted the inclusion of an article in this special issue explaining the ICRP-recommended method for bone marrow dosimetry.Comment: 5 page

A pixelated silicon telescope for solid state microdosimetry

Abstract A solid state microdosimeter consisting of a matrix of cylindrical Δ E elements of micrometric size implanted on a single E stage is discussed in this work. This detector was constructed in order to minimize some discrepancies found when comparing the distribution of energy imparted per event of a single Δ E -stage telescope with the one measured by a cylindrical tissue-equivalent proportional counter (TEPC). These discrepancies were ascribed to geometrical effects related to the wide sensitive area (1 mm2) of the single Δ E -stage telescope. Preliminary irradiations with mono-energetic neutrons showed a better agreement between the spectra measured with the new telescope and the TEPC. The improvement of the procedures adopted for correcting the spectra for tissue equivalence and for the effects due to the track distribution is also discussed

Secondary Neutron and Photon Dose in Proton Therapy

Abstract Background and purpose : The dose due to secondary neutrons and photons in proton therapy was estimated with Monte Carlo simulations. Three existing facilities treating eye and deep-seated tumours were taken into account. The results of the calculations related to eye proton therapy were verified with measurements. Materials and methods : The simulations were performed with the FLUKA code. Neutron fluence was measured inside an Alderson phantom (type ART) with activation techniques. Results : The maximum dose due to secondaries produced in a passive beam delivery system was estimated to be of the order of 10 −4 and 10 −2 Gy per therapy Gy for eye and deep tumour treatments, respectively. In the case of irradiations of deep-seated tumours carried out with an active system, the dose was of the order of 10 −3 Gy per therapy Gy. Conclusions : The dose due to secondaries depends on the geometry of the beam delivery system and on the energy of the primary beam and is lower in the healthy tissues distant from the target volume

Characterization of the energy distribution of neutrons generated by 5 MeV protons on a thick beryllium target at different emission angles.

Neutron energy spectra at different emission angles, between 0° and 120° from the Be(p,xn) reaction generated by a beryllium thick-target bombarded with 5 MeV protons, have been measured at the Legnaro Laboratories (LNL) of the Italian National Institute for Nuclear Physics research (INFN). A new and quite compact recoil-proton spectrometer, based on a monolithic silicon telescope, coupled to a polyethylene converter, was efficiently used with respect to the traditional Time-of-Flight (TOF) technique. The measured distributions of recoil-protons were processed through an iterative unfolding algorithm in order to determine the neutron energy spectra at all the angles accounted for. The neutron energy spectrum measured at 0° resulted to be in good agreement with the only one so far available at the requested energy and measured years ago with TOF technique. Moreover, the results obtained at different emission angles resulted to be consistent with detailed past measurements performed at 4 MeV protons at the same angles by TOF techniques

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

dosimetry methods in boron neutron capture therapy

Dosimetry studies have been carried out at thermal and epithermal columns of LVR- 15 research reactor for investigating the spatial distribution of gamma dose, fast neutron dose and thermal neutron fluence. Two different dosimetry methods, both based on solid state detectors, have been studied and applied and the accuracy and consistency of the results have been inspected. One method is based on Fricke gel dosimeters that are dilute water solutions and have good tissue equivalence for neutrons and also for all the secondary radiations produced by neutron interactions in tissue or water phantoms. Fricke gel dosimeters give the possibility of separating the various dose contributions, i.e. the gamma dose, the fast neutron dose and the dose due to charged particles generated during thermal neutron reactions by isotopes having high cross section, like 10B. From this last dose, thermal neutron fluence can be obtained by means of the kerma factor. The second method is based on thermoluminescence dosimeters. In particular, the developed method draw advantage from the different heights of the peaks of the glow curve of such phosphors when irradiated with photons or with thermal neutrons. The results show that satisfactory results can be obtained with simple methods, in spite of the complexity of the subject. However, the more suitable dosimeters and principally their utilization and analysis modalities are different for the various neutron beams, mainly depending on the relative intensities of the three components of the neutron field, in particular are different for thermal and epithermal columns

Shielding of Proton Accelerators

none3S. Agosteo; M. Magistris; M. SilariGIULINI CASTIGLIONI AGOSTEO, STEFANO LUIGI MARIA; M., Magistris; M., Silar