117 research outputs found
TOPAS simulations of the response of a mini-TEPC: benchmark with experimental data
No full textObjective. Microdosimetry offers a fast tool for radiation quality (RQ) verification to be implemented in treatment planning systems in proton therapy based on variable LET or RBE to move forward from the use of a fixed RBE of 1.1. It is known that the RBE of protons can increase up to 50% higher than that value in the last few millimetres of their range. Microdosimetry can be performed both experimentally and by means of Monte Carlo (MC) simulations. This paper has the aim of comparing the two approaches. Approach. Experimental measurements have been performed using a miniaturized Tissue equivalent proportional counter developed at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics with the aim of being used as RQ monitors for high intensity beams. MC simulations have been performed using the microdosimetric extension of TOPAS which provides optimized parameters and scorers for this application. Main results. Simulations were compared with experimental microdosimetric spectra in terms of shape of the spectra and their average values. Moreover, the latter have been investigated as possible estimators of LET obtained with the same MC code. The shape of the spectra is in general consistent with the experimental distributions and the average values of the distributions in both cases can predict the RQ increase with depth. Significance. This study aims at the comparison of microdosimetric spectra obtained from both experimental measurements and the microdosimetric extension of TOPAS in the same radiation field.This work was supported by the 5th Scientific Commission of the Italian Institute for Nuclear Physics(INFN), the Belgian nuclear research Centre SCK•CEN and Hasselt University. This work has been partially supported by the ENEN + project that has received funding from the EURATOM research and training Work Programme 2016-2017-1 #755576
The effect of different lower detection thresholds in microdosimetric spectra and their mean values
No full textResearch on the applications of microdosimetry to particle therapy is spreading worldwide with a rapid increase of publications in the last years. In order to be able to perform an intercomparison of data acquired with different detectors in different clinical centres it is important to analyse data with a standard procedure. Often microdosimetric spectra are presented with different lower detection thresholds, in relation with different detection sensitivity and noise levels. The purpose of this paper is to analyse the influence of the lower detection threshold on the dose-mean lineal energy values, which are used as an assessment of the average LET of the radiation field. Furthermore, the dose distribution of the lineal energy can be used in combination with biological weighting functions to estimate the biological RBE at different positions along the penetration depths of therapeutic proton or carbon ion beams. Microdosimetric spectra cut at different lower thresholds lead in principle to different RBE values. It was an additional purpose of this work to analyse and discuss this effect both for proton and carbon ion irradiations. Spectra in proton and carbon ion beams gathered with a miniaturized TEPC developed at the Legnaro National Laboratories of the Italian Institute for Nuclear Physics (LNL-INFN) have been used to perform this study. Linear extrapolation of the microdosimetric spectra to a common value of 0.01 keV/um significantly reduces the deviations in the mean values due to different lower thresholds. It is advisable to perform this procedure to uniform the data analysis and facilitate the intercomparison of data.This work was supported by the 5th Scientific Commission of the Italian Institute for Nuclear Physics (INFN), the Belgian Nuclear Research Centre SCK CEN and Hasselt University. This work has been partially supported by the ENEN + project that has received funding from the EURATOM research and training Work Programme 2016–2017 – 1 #755576
Radiation Measurements / Uncertainty evaluation for organ dose assessment with optically stimulated luminescence measurements on mobile phone resistors after a radiological incident
No full textA radiological incident may result in members of the public being exposed to high doses of ionizing radiation. Rapid triage and a rough dose assessment is then an important component of the process of identifying people requiring immediate medical attention, supporting clinical observations and widening the scope to categorize those individuals who are potentially exposed but are pre-symptomatic. Optically stimulated luminescence on mobile phone resistors is well established in this context. Previous studies have shown good dosimetric properties and dose reconstruction protocols were optimized in the MULTIBIODOSE project (Bassinet et al., 2014). Evaluation of the full uncertainty budget and the detection limit is of fundamental importance for any personal dosimetry technique. In this work it was investigated how different factors influence the organ dose assessment with optically stimulated luminescence on mobile phone resistors, how one can correct for these, and how much they contribute to the uncertainty. The investigated factors include calibration, zero dose signal, reproducibility, dose response, fading, red light exposure, storage temperature, energy response and conversion from resistor dose to organ dose depending also on exposure scenario and mobile phone position. The uncertainty and detection limit were found to depend strongly on the delay between incident exposure and measurement and knowledge of the incident scenario. The uncertainty also depends strongly on the dose level. Detection limits of the order of 100 mGy were found, which is more than sufficient for triage. For doses around the detection limit the uncertainties related to the zero dose signal and reproducibility are dominant, while for higher doses of the order of grays the uncertainties related to fading and conversion from resistor to organ doses are dominant. For the higher doses the uncertainties are around 50% (k = 2) for known incident scenarios and up to more than 100% (k = 2) for unknown scenarios. Based on the results from this work recommendations are given to further decrease the uncertainty and detection limit for this technique.Olivier Van Hoey, Demi Romkens , Jonathan Eakins, Eftychia Kouroukla, Michael Discher, Filip Vanhaver
Use of active personal dosimeters in hospitals: EURADOS survey
No full textConsidering that occupational exposure in medicine is a matter of growing concern, active personal dosimeters (APDs) are also increasingly being used in different fields of application of ionising radiation in medicine. An extensive survey to collect relevant information regarding the use of APDs in medical imaging applications of ionising radiation was organised by the EURADOS (European Radiation Dosimetry Group) Working Group 12. The objective was to collect data about the use of APDs and to identify the basic problems in the use of APDs in hospitals. APDs are most frequently used in interventional radiology and cardiology departments (54%), in nuclear medicine (29%), and in radiotherapy (12%). Most types of APDs use silicon diodes as the detector; however, in many cases their calibration is not given proper attention, as radiation beam qualities in which they are calibrated differ significantly from those in which they are actually used. The survey revealed problems related to the use of APDs, including their reliability in pulsed x-ray fields that are widely used in hospitals. Guidance from regulatory authorities and professional organisations on the testing and calibration of APDs used in hospital would likely improve the situation
Instruments for Personal Dosimetry of External Radiation: Present Situation in Europe and Future Needs
No full textMICRODOSIMETRIC MODELING OF THE RELATIVE LUMINESCENCE EFFICIENCY OF LiF:Mg,Ti (MTS) DETECTORS EXPOSED TO CHARGED PARTICLES
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Instruments for Personal Dosimetry of External Radiation: Present Situation in Europe and Future Needs
No full textAbstract ID: 73 Design of a personal dosimeter for estimating the effective dose of medical staff when wearing radioprotective garments using Monte Carlo simulations
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