Papers by Andrzej Kacperek
Medical Physics, Jun 1, 2012
PURPOSE To measure the calibration curves of EBT3 dosimetry films in photon and proton beams and ... more PURPOSE To measure the calibration curves of EBT3 dosimetry films in photon and proton beams and to quantify the related uncertainties from one beam type to another. METHODS EBT3 Gafchromic films have similar properties than EBT2 with a symmetric construction and a matte polyester substrate to prevent Newton's ring artefacts. Films from a same batch were exposed in three different beam qualities, an Elekta SL25 6 MV photon beam, a 100 MeV 5×5cm2 proton beam delivered by pencil-beam scanning dedicated system from IBA and a 60 MeV fixed proton beam (2.5cm in diameter) at Clatterbridge Center for Oncology (CCO), UK. The films were read using an EPSON 10000 XL/PRO scanner. Film calibration curves were acquired for all modalities within a range of 0.05 to 20 Gy. Influence of increasing linear-energy transfer (LET) on film response was investigated by comparing dose measured by EBT3 to a silicon diode detector in depth for a fully-modulated beam using the CCO beam line (homogeneous dose with distal end at 3.1cm in water). A comprehensive uncertainty budget (reproducibility, uniformity'¦) was estimated on films irradiated by Elekta SL25. RESULTS The main source of uncertainty was the non-uniformity of the scanner response. By placing all the irradiated films at the center of the scanner, the uncertainty could be reduced from 5.8% to 1.9% (1 sigma). For all beams and energies, the calibration curves were matched within uncertainties. Along the fully-modulated depth dose curve, diode and EBT3 measurement were in a 4% agreement point-to-point, indicating films weak dependence with LET. CONCLUSIONS The weak influence of LET, beam type and energy on film response as well as its small uncertainty make EBT3 suitable for relative dosimetry and a promising candidate for measuring correction factors (quality, recombination,'¦) for reference dosimetry with ion chambers of non-standard beams (e.g pencil-beam scanning proton-therapy). “This work is supported by the Walloon Region under the project name InVivoIGT, convention number 1017266.â€.
Journal of Instrumentation, Jan 25, 2018
Journal of Instrumentation, Nov 30, 2017
Ophthalmology, May 1, 2023
This paper describes recent work using GEANT4 to simulate monoenergetic proton beams (50 MeV, 150... more This paper describes recent work using GEANT4 to simulate monoenergetic proton beams (50 MeV, 150 MeV and 250 MeV) and the 62 MeV ocular proton beam line at the Clatterbridge Centre for Oncology (CCO). GEANT4 results are compared with those obtained using other Monte Carlo codes (MCNPX, PTRAN, and SRIM) and measurement, including depth-dose data and radial dose and energy distributions at two different depths. GEANT4 and PTRAN are in generally good agreement but differences in both the depth and height of the Bragg peak become more apparent at higher energies due to the parameterisation in GEANT4 of stopping power data taken from ICRU 49, and by some differences in their inelastic nuclear interaction cross-section data. Other variations at the energies under consideration are accounted for by PTRAN's lack of secondary proton transport. GEANT4 is in better agreement with MCNPX at all energies but again differences in the nuclear interaction data result in MCNPX giving a higher relative dose compared to GEANT4 at depths below the Bragg peak. The different multiple scattering model used in MCNPX also tends to give broader radial dose distributions and significantly larger tails in the energy distributions in water compared to GEANT4. Further simulations of depth dose and radial dose distributions in PMMA are compared with diode and film measurements on the CCO ocular proton beam line. GEANT4 overestimates the height of the Bragg peak for the full-energy beam by around 20% and gives a slightly increasing (instead of a flat) dose profile for the modulated beam with a distinctive peak near the end of the range. Radial dose profiles are in reasonable agreement with measurement although GEANT4 produces a sharper penumbra. However, daily variations in the beam output and the type of detector have a significant effect on the measured data.
Medical Physics, Jun 1, 2012
PURPOSE The IAEA TRS-398 code of practice can be applied for the measurement of absorbed dose to ... more PURPOSE The IAEA TRS-398 code of practice can be applied for the measurement of absorbed dose to water under reference conditions with an ionization chamber. For protons, the combined relative standard uncertainty on those measurements is less than 2% while for light-ion beams, it is considerably larger, i.e. 3.2%, mainly due to the higher uncertainty contributions for the water to air stopping power ration and the W air-value on the beam quality correction factors kQ,Q0 . To decrease this uncertainty, a quantification of kQ,Q0 is proposed using a primary standard level graphite calorimeter. This work includes numerical and experimental determinations of dose conversion factors to derive dose to water from graphite calorimetry. It also reports on the first experimental data obtained with the graphite calorimeter in proton, alpha and carbon ion beams. METHODS Firstly, the dose conversion has been calculated with by Geant4 Monte-Carlo simulations through the determination of the water to graphite stopping power ratio and the fluence correction factor. The latter factor was also derived by comparison of measured ionization curves in graphite and water. Secondly, kQ,Q0 was obtained by comparison of the dose response of ionization chambers with that of the calorimeter. RESULTS Stopping power ratios are found to vary by no more than 0.35% up to the Bragg peak, while fluence correction factors are shown to increase slightly above unity close to the Bragg peak. The comparison of the calorimeter with ionization chambers is currently under analysis. For the modulated proton beam, preliminary results on W air confirm the value recommended in TRS-398. Data in both the non-modulated proton and light-ion beams indicate higher values but further investigation of heat loss corrections is needed. CONCLUSIONS The application of graphite calorimetry to proton, alpha and carbon ion beams has been demonstrated successfully. Other experimental campaigns will be held in 2012. This work is supported by the BioWin program of the Wallon Government.
Physics in Medicine and Biology, Apr 13, 2017
The Journal of Nuclear Medicine, 2001
The prompt gamma-ray analysis of 14 biologically interesting elements was performed using a relat... more The prompt gamma-ray analysis of 14 biologically interesting elements was performed using a relatively weak reactor neutron flux 3 x 104 n.cm-2.s-1. Sample irradiations were performed in air and in a water phantom, to obtain sensitivity limits of the elements prior to possible use in in-vivo neutron activation analysis. A comparison was performed between prompt gamma-ray measurement by a Nal(Tl) and Ge(Li) detector, and also between high and low-energy regions. Only Cd, Cl and Hg samples yielded minimum detection limits less than 100mg for irradiations in air, and only Cd remained in this category following irradiation in the water phantom. Preliminary studies were performed of irradiated sample depth measurement, in the water phantom, in order to provide a tissue attenuation correction factor. A comparison was made between the double gamma-ray and scatter-to-peak (SPR) depth measurement techniques. A formula was developed for a point source measured by a parallel collimated gamma-c...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
Inner-Shell and X-Ray Physics of Atoms and Solids, 1981
Quantitative measurement of low-energy X rays with Si(Li) detectors is hampered by lack of suitab... more Quantitative measurement of low-energy X rays with Si(Li) detectors is hampered by lack of suitable calibration sources. Usually, a set of X-ray standards, of defined energy and known source strength of about 106 to 107s-1 , is required. The final uncertainty on their calibration should be better than 5 %. Various sophisticated methods have been proposed for low-energy efficiency determination 1–13 . Generally, these methods do not yield accuracies better than 10 % at photon energies below 5 keV. This paper describes a method to prepare and standardize sources which would be simple to use for calibration of solid state detectors at energies below 4 keV and which should be capable for higher accuracy. It is based on fluorescence excitation of elemental foils of low atomic number by a suitable X-ray source which is evaporated, in a well defined area of 5 mm diameter, directly onto the foil. In this way, a physically robust and compact ensemble can be supplied. The standardization is done by a defined solid angle flow proportional counter. Due to the high absorption of these low-energy X rays there is an anisotropy which becomes more prominent at larger solid angles.
Medical Physics, 2002
Small dosimeters as solid state detectors can be useful for the dosimetric characterization and p... more Small dosimeters as solid state detectors can be useful for the dosimetric characterization and periodic quality control of radiotherapy proton beams. The calibration of solid state detectors for proton beams is not a solved problem especially for ophthalmologic proton beams, where these detectors present a LET‐dependent signal. In this work a PTW diamond detector has been selected because of its good signal reproducibility (0.3%) and stable response with accumulated dose. A method that takes into account the LET dependence of the diamond detector signal, at 62 MeV proton beam, is here proposed. In particular an empirical correction factor, has been determined as a function of the residual range quality index, to correct the diamond detector signal for a proton beam of incident effective energy A dedicated software allows us to use the diamond detector as an on‐line reference dosimeter, where an ionization chamber may be difficult to use, or for periodic quality control procedures. ...
Biochemical Society Transactions, Nov 1, 1996
Medical Physics, Jun 1, 2016
PURPOSE For photon and electron beams, the standard device used to measure absorbed dose is a cal... more PURPOSE For photon and electron beams, the standard device used to measure absorbed dose is a calorimeter. Standards laboratories are currently working on the establishment of graphite calorimeters as a primary standard for proton beams. To provide a practical method for graphite calorimetry, it is necessary to convert dose to graphite to dose to water, requiring knowledge of the water-to-graphite stopping-power ratio and the fluence correction factor. This study aims to present a novel method to determine fluence corrections experimentally, and to apply this methodology to low- and high-energy proton beams. METHODS Measurements were performed in 60 MeV and 180 MeV proton beams. Experimental information was obtained from depth-dose ionization chamber measurements performed in a water phantom. This was repeated with different thicknesses of graphite plates in front of the water phantom. One distinct advantage of this method is that only ionization chamber perturbation factors for water are required. Fluence corrections were also obtained through Monte Carlo simulations for comparison with the experiments. RESULTS The experimental observations made in this study confirm the Monte Carlo results. Overall, fluence corrections between water and graphite increased with depth, with a maximum correction of 1% for the low-energy beam and 4% for the high-energy beam. The results also showed that a fraction of the secondary particles generated in proton therapy beams do not have enough energy to cross the ionization chamber wall; thus, their contribution is not accounted for in the measured fluence corrections. This effect shows up as a discrepancy in fluence corrections of 1% and has been confirmed by simulations of the experimental setup. CONCLUSION Fluence corrections derived by experiment do not account for low-energy secondary particles that are stopped in the ion chamber wall. This work will contribute to a practical graphite calorimetry technique for determining absolute dose to water in proton beams.
We present simulations and measurements of Cerenkov optical radiation in electron and proton radi... more We present simulations and measurements of Cerenkov optical radiation in electron and proton radiotherapy. Photographs of Cerenkov emission from electrons can predict the range to ±1.5mm, but underestimate superficial dose.
Nuclear Medicine Communications, Mar 1, 2002
Uploads
Papers by Andrzej Kacperek