VERIDIC: validation and estimation of radiation skin dose in interventional cardiology

Interventne procedure u radiologiji i kardiologiji povezani su sa visokim dozama za kožu pacijenta i potencijalnim radijacionim povredama kože. Različita metodologije i rešenja razvijene us za procenu maksimalne doze za kožu, čija se svojsvta, uključujuši i tačnost značajno razlikuju. U radu su prokazani ciljevi, metode i preminiran a rešenja projekta VERIDIC usmerenoj na validaciju zaličitih ofline i online softvera za procenu doze za kožu pacijenta u intervenatnoj kardiologiji.In interventional cardiology (IC), patients may be exposed to high doses to the skin resulting in tissue reactions (skin burns) following single or multiple procedures. To address this issue, online and offline software has been developed to estimate the maximum skin dose (MSD) to the patient from IC procedures. However, the capabilities and accuracy of such skin dose calculation (SDC) software to estimate MSD and 2D dose distributions markedly differ among vendors. Hence, this project focuses onthe harmonisation of RDSR (radiation dose structured report) and on the validation of SDC software products in IC, which will optimise radiation protection of patients. The outcome of the project will include the standards for digital dose reporting, development of protocols for acceptance testing and Quality Control (QC)of SDC software and setting of diagnostic reference levels per clinical complexity, assessing thefrequency of high-dose procedures as well as dose reduction strategies based on the multi-centric data collection. This paper focuses on the work performed to investigate performance of solid state dosimeters used in clinical environment.Proceedings: [http://vinar.vin.bg.ac.rs/handle/123456789/8681]XXX симпозијум ДЗЗСЦГ (Друштва за заштиту од зрачења Србије и Црне Горе), 2- 4. октобар 2019. године, Дивчибаре, Србиј

Comparison of measured and calculated spectra emitted by the X-ray tube used at the Gustave Roussy radiobiological service

International audienceAlong with the strengthening of the control processes of irradiation systems used in industrial and medical sectors, direct measurement of spectra emitted by X-ray tubes is becoming a necessity to ensure beam quality. To reach that aim, a research project was initiated at the Henri Becquerel Laboratory to develop a system to measure, with semiconductor detectors (Ge and CdTe), the spectra emitted by X-ray tubes. However, the measured spectra are distorted by artifacts associated with the detection processes. Therefore, two algorithms were developed to correct for the pile-up distortions due to the high count rate and for the photon escape phenomenon, which takes place into the crystal of the semiconductor detectors. Our system was tested using the X-ray tube used by the Gustave Roussy (France) radiobiological service. Measurements with two high voltages (70 and 200 kV) were carried out using a CdTe detector equipped with a micrometric positioning system and a specific collimator to reduce the high count rate. The measured and calculated spectra using the XCOMP5 and SpeKcalc V1.0 programs were compared. This comparison reveals a good agreement

Characterization of an innovative detector based on scintillating fiber for personalized computed tomography dosimetry

International audienceFor technical and radioprotection reasons, it has become essential to develop new dosimetric tools adapted to the specificities of computed tomography (CT) to ensure precise and efficient dosimetry since the current standards are not suitable for clinical use and for new CT technological evolution. Thanks to its many advantages, plastic scintillating fibers (PSF) is a good candidate for more accurate and personalized real-time dosimetry in computed tomography, and the company Fibermetrix has developed a new device named IVISCAN ® based on this technology. In this study, we evaluated performances of IVISCAN ® and associated uncertainties in terms of dose-rate dependence, angular dependence, stability with cumulative dose, repeatability, energy dependence, length dependence, and special uniformity in reference and clinical computed tomography beam qualities. For repeatability, the standard deviation is less than 0.039%, and the absolute uncertainty of repeatability lies between 0.017% and 0.025%. The deviation between IVISCAN ® and the reference regarding energy dependence is less than 1.88% in clinical use. Dose rate dependence results show a maximum deviation under ±2%. Angular dependence standard deviation σ is 0.8%, and the absolute uncertainty was 1.6%. We observed 1% of variation every 50 Gy steps up to a cumulative dose of 500 Gy. Probe response was found to be independent of the PSF length with a maximum deviation ∆D size < 2.7% between the IVISCAN ® probe and the 1 cm PSF probe. The presented results demonstrated that IVISCAN ® performances are in accordance with metrology references and the international standard IEC61674 relative to dosemeters used in X-ray diagnostic imaging and then make it an ideal candidate for real-time dosimetry in CT applications

Determination of the efficiency of high purity germanium and silicon diode detectors for improved assessment of emission spectra delivered by medical X-ray tubes

International audienceX-ray sources are widely used in medicine: brachytherapy, radiodiagnosis, mammography and contact radiotherapy. Kerma in air is the primary quantity measured to determine the dose to the patient. Accurate air kerma assessment is obtained using correction factors calculated using the emission spectrum. The Laboratoire National Henri Becquerel launched an in-depth study of the spectral emission of its reference X-ray beams used in dosimetry. Two semiconductor detectors are discussed here: a High-Purity germanium and a silicon PiN, both cooled and operated with dedicated electronics and software. In the low energy range (E < 50 keV), those spectrometers are complementary but require a careful calibration to deduce the emitted spectrum from the detected one. Indeed, both detectors were characterized in terms of spectral response and intrinsic efficiency using a tuneable monochromatic X-ray source (SOLEX at CEA Saclay) in the 5- to 20-keV energy range and various radionuclides. The characterization methods and results, including the first measured spectra of medical X-ray tubes (high voltage < 50 kV), are presented in this work. This paper presents the first step of a broader project, aiming at assessing the emission spectrum independently of the detector choice

Design d'une installation d'étalonnage pour la dosimétrie d'environnement photonique

International audienceHors situations accidentelles les débits d'équivalent de dose ambiant mesurés en France dans l'environnement représentent en moyenne quelques dizaines de nSv/h. L'étalonnage des appareils utilisés pour ces mesures, installés à poste fixe autour des installations ou non, doit être réalisé face à des débits d'équivalent de dose ambiant voisins de ceux qu'ils mesureront. Afin d'atteindre un niveau d'incertitude compatible avec les besoins métrologiques pour l'étalonnage et le test des appareils de mesure, il est donc nécessaire de disposer d'installation dites à bas bruit de fond, soit inférieur d'environ un facteur 10 par rapport au bruit de fond naturel.S'inspirant d'une installation japonaise existante le LNHB a décidé de mettre en place un tel faisceau de photons au sein d'une enceinte blindée. Une mesure spectrométrique a permis d'identifier et de quantifier les composantes du bruit de fond radiatif naturel. Partant de ce résultat, l'épaisseur et la nature des parois ont été déterminées au moyen de calculs Monte Carlo pour lesquels on décrira les hypothèses de calcul et les résultats obtenus.Les dimensions internes de l'enceinte blindée ainsi que l'ouverture de collimation du champ de rayonnement onr aussi été modélisées au moyen de calcul Monté Carlo afin de trouver un équilibre entre le rayonnement direct et le rayonnement diffusé à l'intérieur de l'enceinte tout en permettant l'irradiation de la totalité des dosimètres à étalonner

Design of a low dose rate calibration facility for environmental radiation protection dosimetry

International audienceIntroductionIn normal situations, the natural H*(10) rates measured in France in the environment represent on average a few tens of nSv/h. The calibration or verification of the devices used for these measurements must be performed with H*(10) rates close to those to be measured. In order to reach a level of uncertainty compatible with the metrological needs. Low background facilities are therefore necessary, i.e. lower by a factor of about 10 compared to the natural background.Methods and ResultsInspired by an existing Japanese facility and following the main specifications of the ISO FDIS 20956 standard, the LNHB decided to set up a photon beam within a shielded box (1mx1mx1.2m) in which the natural radiative level is reduced by at least a factor of 10. The steps of the installation and the characterization of the photon beams within this shielded box are described. The identification and the spectrometric characterization up to 2 MeV of the components of the natural radiative background allow choosing 25 mm thick lead walls, by means of Monte Carlo calculations. The calculations show a theoretical decrease of almost 2 decades of the background inside the box. The calculation of the theoretical H*(10) rate led to install two 60Co photon sources of 50 and 300 kBq. The collimator opening gives a beam radius of 15 cm at the reference plane located at 40 cm with a scattered radiation component of about 15% at the measurement point and a profile varying by about 18% between the edge and the center of the beam in terms of dose equivalent. This collimator would be optimized to lower these values. The traceability of the dose equivalent measurements to the French primary reference in terms of air kerma is achieved by calibrating a BERTIN type 6150AD survey meter in a collimated photon beam with higher dose rates.ConclusionsThe results of the modelling are compared to the measurements and the uncertainty budget is evaluated following the ISO 13005 guide method

Assessment of the impact on an OSL dosimetry system of the new operational dose quantities proposed in the ICRU 95

International audienceIn 2020, a new ICRU report on Operational Quantities for External Radiation Exposure was presented by ICRP. This document presents a new concept for definition of the operational quantities which is radically different to the previous ICRU concept. This change will impact the metrology of occupational dosimetry for the radiation protection of the worker. For instance, the conversion coefficients (personal dose equivalent / fluence) for photons change significantly below 50 keV up to a factor exceeding 5. The work presented consist to assess the impact on an individual dosimetry system for photon exposure based on an OSL technology with Al2O3:C sensor. This impact is analysed considering the criteria of the EN62387:2016 (which defined the performance and test requirements for personal dosimetry). It will be presented also a retrospective impact on the dose reported on the previous monitoring periods at the French Landauer laboratory

Estimation de l'incertitude globale associée à une référence en terme de dose dans l'eau pour la curiethérapie bas débit de dose.

Depuis 2006, le LNE-LNHB a entrepris de mettre au point une référence primaire pour la curiethérapie bas débit de dose traitant des cancers prostatiques et ophtalmiques. Le détecteur à la base de cette référence est d'une conception innovante puisqu'il s'agit d'une chambre d'ionisation à parois d'air de forme toroïdale. Le but de cette référence est de déterminer la dose absorbée dans l'eau pour les grains de curiethérapie à l'iode 125 (énergie de la raie initiale la plus énergétique égale à 35,5 keV). Dans le cadre de la mise en place de cette référence, des calculs Monte Carlo ont été effectués à l'aide de trois codes afin de déterminer la valeur du facteur de conversion nécessaire à l'établissement de la référence primaire ainsi que son incertitude. Ce facteur, spécifique de la méthodologie de détermination, permet le passage des conditions de mesure à celles de référence telles que décrites par l'AAPM. Les codes egspp (code EGSnrc version V4-r2-3-2), MCNP (version 1.40) et PENELOPE (version parallèle MPI de la distribution PENELOPE 2006) ont été utilisés dans ce but. Le facteur de conversion (comprenant sa valeur et son incertitude) a été déterminé à partir de l'écart-type expérimental sur les valeurs des facteurs de conversion calculées à l'aide de ces trois codes

Dosimetry formalism and calibration procedure for electronic brachytherapy sources in terms of absorbed dose to water

International audienceThe LNE-LNHB has developed a methodology to standardize electronic brachytherapy sources in terms of absorbed dose to water. It is based on the measurement of the air-kerma rate at a given distance from the source and the Monte Carlo calculation of a conversion factor. This factor converts the air kerma in measurement conditions into absorbed dose to water at a 1 cm reference depth in a water phantom. As a first application, the method was used to calibrate a Zeiss INTRABEAM system equippedwith its 4 cm diameter spherical applicator. The absorbed-dose rate value obtained in the current study was found significantly higher than that provided by the manufacturer in line with the observations already reported by a few other teams

Comprehensive validation of a Monte Carlo kV-CBCT model using OSL and spectral measurements

International audiencePurpose or Objective: The use of Cone-Beam computed Tomography (CBCT) is progressively increasing in radiotherapy treatments, but additional doses induced are not well quantified and could amplify the risk for patients to develop a second cancer. There is a need, expressed by the medical physics community, to develop tools to estimate, report and potentially help reducing CBCT doses. We hence developed a Monte Carlo (MC) model for the XVI kV-CBCT system. The dosimetric and geometric accuracy of the simulated beams was evaluated by comparisons withmeasurements in a water tank, and x-ray energy spectra acquisitions. Before clinical use, the model requires an evaluation in anthropomorphic phantoms in which were inserted OSL NanoDots (Landauer). The purpose of the present study is to develop an accurate dosimetric protocoltaking into account for OSL energy dependence in keV energy range.Material and Methods: A MC model of the XVI was developed using the PENELOPE code. The dosimetric and geometrical evaluation of the beam MC models was performed by comparing simulations with lateral and depth-dose profiles measured using a PTW Farmer-type chamber, and on-axis energy spectra measured with a CdTe detector. These comparisons were performed at 120, 100 and 80 kVp, and for different filtration/collimation couples. For OSL measurements, the first step was to perform, in different beam qualities, in-air cross-calibrations with a PTW Farmer type chamber. At this energy range, OSL exhibit strong energy dependence, so the signal needs to be corrected for the spectral variations between calibration and measurement conditions. Thus, to ensure accurate dose measurements, a correction method was developed using calculated spectra. The dosimetric protocol was validated by performing dose profiles with OSL inserted in a PMMA tube submerged in water. Preliminary comparisons with XVI model were made with acquisitions in a home-made heterogeneous phantom consisting of a water tank equipped with PMMA, bone and lung equivalent inserts.Results: Experimental and simulated lateral and depth-dose profiles, and energy spectra, are in excellent agreement (Fig 1A).These results validate that the MC model accurately reproduces the dosimetric and geometric properties of the XVI beams. The uncorrected OSL profiles in the PMMA tube over-estimate by 15 % the calculated doses. However, energy corrected measurements are matching the simulations and the differences not exceed 7.5 % (Fig 1B and 1C). Table 1 presents doses measured at different points in the heterogeneous phantom and discrepancies not exceed 11.3 %.Conclusion: The dosimetric protocol developed for OSL allows accurate measurements of imaging doses, and will be then used to validate the dose calculation tool in pre-clinical conditions. Preliminary results obtained in the home-made phantom highlight the accuracy of XVI MC model. Further validations are on-going in anthropomorphic phantoms