323,038 research outputs found
Detectors for measurement of microdosimetric quantities
No full textMicrodosimetric quantities have been used for assessing the radiation quality of hadron therapy fields since long. They are stochastic quantities whose distributions depend on the fluctuations of energy deposition in cellular and/or sub-cellular structures. The present work overviews the detectors which are used mainly for assessing the radiation quality of hadron therapy fields (protons and carbon ions), discussing their advantages and limitations based on the author’s experience. The microdosimeters which are described and discussed herein are, in particular, tissue-equivalent proportional counters (TEPCs), gas detectors based on gas-electron multiplication (GEMs), silicon and diamond detectors
A Feasibility Study for BNCT of Skin Melanoma with an Accelerator - Based Neutron Source
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Decommissioning-Oriented Design of Concrete Bunker in a Medical Cyclotron Facility: A Case Study
No full textNumerical modeling of the gas gain of low-pressure Tissue-Equivalent Proportional Counters
No full textProportional counters are radiation detectors widely used in many applications. The design of the counter, to best fit each application, needs an accurate knowledge and physical modeling of the electron avalanche process. A particular proportional counter is the tissue-equivalent proportional counter (TEPC), the reference detector for experimental microdosimetry, which consists of a spherical or cylindrical chamber filled with low-density tissue-equivalent gas to simulate the energy deposition in tissue sites of micrometric size. The lower operation limit of standard TEPCs operated in the pulse-height analysis mode is about 0.3μm. In order to overcome this technological limit, different avalanche-confinement nano-microdosimetric TEPCs capable of measuring microdosimetric spectra in the nanometric domain were designed and constructed. In this work, a novel numerical tool developed for the Monte Carlo simulation of the electron avalanche process inside a low-pressure TEPC is described. The Monte Carlo code allows to simulate complex 3D electric field configurations exploiting COMSOL finite elements analysis. Several models for the electron interactions (i.e. scattering and ionization) are included in the code. The code has been benchmarked with the experimental results of a wall-less avalanche-confinement TEPC in terms of absolute gas gain for different operating conditions (i.e. gas pressures and electrode voltages). The results show that the code is capable of reproducing the absolute value of the gas gain for the avalanche-confinement TEPC simulating some tenths of nanometers in site size. Moreover, the code can reproduce both the extension and the shape of the proportional counter working windows. The code was also applied for simulating the probability of absorption of electrons by the central third electrode: the helix. The results show a non-negligible probability of absorption in the common range of operation. This code will be further applied for optimizing the TEPC design, capable of simulating site sizes closer to the nanometer region
A Cyclotron Based Solution for a BNCT Source
No full textThe present paper proposes and preliminarily discusses the possibility to produce thermal fluxes of sufficient intensity for BNCT (explanted liver and skin melanoma) and BNCS (rheumatoid arthritis), using commercial cyclotrons conceived for radioisotopes production. Application of BNCT to the treatment of liver and melanoma require a thermal neutron fluence of about 5 10E12 cm-2, that correspond to a thermal fluence rate of the order of about 1.5 10E09 cm-2 s-1 for one hour irradiation. In the case of BNCS about 5 10E11 cm-2 are required, that correspond to a thermal fluence rate of the order of about 10E9 cm-2 s-1 for 10 minutes irradiation. Purpose of this preliminary study is to verify the current requirements to obtain the needed thermal fluence rate. This study is necessary before proceeding to the optimisation of the moderating structure and to the experimental tests
Microdosimetry at nanometric sites of charged Helium, Carbon and Oxygen beams with an advanced Tissue Equivalent Proportional Counter
No full textThe effectiveness of radiotherapy, particularly hadron therapy, is closely tied to the interactions of radiation at the cellular and sub-cellular levels. Understanding the local energy deposition of charged particles is essential for accurately predicting their biological effects. Traditional dosimetric approaches, based on absorbed dose, fail to describe the stochastic nature of energy deposition at micrometric and nanometric scales. This study investigates the micro- and nano-dosimetric properties of Helium, Carbon, and Oxygen ion beams at 62 MeV/u using an advanced Tissue Equivalent Proportional Counter (TEPC). This TEPC, designed to simulate site sizes ranging from 0.5 μm to 25 nm, was placed at various depths across the Bragg peaks of the ion beams at the INFN-LNS facility in Catania (Italy). Results show a clear dependence of microdosimetric distributions on both simulated site size and position across the depth-dose profile. Smaller site sizes shift the distribution toward higher lineal energies, especially at proximal depths, suggesting that microdosimetric spectra at nanometric scale can offer different insights on the radiation interaction with tissue. This study also underlines the role of secondary electrons and fragmentation effects, which vary with the atomic number of the ion, producing different effects for Helium, Carbon and Oxygen ions. These findings may have significant implications for improving relative biological effectiveness (RBE) models in hadron therapy. By extending microdosimetric analysis to the nanometric scale, this research provides new data for a possible improvement of the predictive accuracy of radiation-induced biological effects. The novel TEPC used in this study bridges the gap between microdosimetry and nanodosimetry, offering a more refined assessment of radiation quality
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