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Nunes LH, Guidelli EJ. Microfluidics unveil nucleation and growth in the radiolytic synthesis of colloidal silver and allow X-ray detection with nanoclusters. Radiat Phys Chem Oxf Engl 1993 2023. [DOI: 10.1016/j.radphyschem.2023.110790] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Use of calculations to validate beam quality and relative dose measurements for a kilovoltage X-ray therapy unit. Phys Eng Sci Med 2022; 45:537-546. [PMID: 35381970 DOI: 10.1007/s13246-022-01120-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Accepted: 03/16/2022] [Indexed: 10/18/2022]
Abstract
Relative dosimetry measurements are required to fully commission kilovoltage X-ray units for superficial and orthovoltage X-ray therapy. Validation of these relative dosimetry measurements with Monte Carlo methods is advantageous being independent of the measurement process. In this study use is made of the X-ray spectrum generating program SpekPy along with the EGSnrc Monte Carlo code to calculate depth doses and explore the dosimetry effect of changes in backscatter. These calculations are compared with previously reported measurements for the Pantak SXT 150 X-ray therapy unit. SpekPy can also be used to generate half value layer (HVL) values and these are also compared to previously reported HVL measurements for the same X-ray therapy unit. It was found that agreements of the order of 5% in HVL, 3% in depth dose and 1% in backscatter doses were found between Monte Carlo calculations and the previously published measured data. Exit doses in conditions of lack of full backscatter were explored with Monte Carlo calculations demonstrating reduced exit dose up to 20% in these conditions. It is concluded that SpekPy with Monte Carlo codes such as EGSnrc provides a straightforward approach to validating various relative dosimetry measurements in kilovoltage X-ray dosimetry.
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Daniel J, Yousif Y, Zifodya J, Hill R. An evaluation of solid state detectors for the relative dosimetry of Kilovoltage x-ray beams. Med Phys 2022; 49:4082-4091. [PMID: 35179232 DOI: 10.1002/mp.15543] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 02/04/2022] [Accepted: 02/07/2022] [Indexed: 11/09/2022] Open
Abstract
INTRODUCTION Kilovoltage (kV) x-ray beams are an essential modality in radiotherapy. Solid state detectors are widely available in radiotherapy departments but their use for kV dosimetry has been limited to date. This study aimed to evaluate the dosimetric performance of a range of solid state detectors for kV dosimetry. METHOD Percentage depth doses (PDDs) and Relative Output Factors (ROFs) were measured on an XStrahl 300 unit (XStrahl-Ltd., UK) using 60, 100, 150 and 300 kVp x-ray beams. The fields were defined by circular applicators with field sizes of 2, 5, 8 and 10 cm diameter and square applicators of field sizes 10×10 and 20×20 cm2 . The following PTW dosimeters were used for measurements: Advanced Markus, PinPoint 3D and Semiflex ionization chambers; Photon, Electron and SRS diodes plus the microDiamond detector. All PDDs were normalized at 5 mm depth and ROFs were measured at 3 mm depth to avoid collisions with the end of the applicators. ROFs measured using chambers were corrected for polarity and ion-recombination effects. RESULTS AND DISCUSSION PDD measurements for 60,100 and 150 kVp beam exhibited good agreement between all diodes and the ionization chambers over the entire range of depths except in the first few millimeters near the surface. However, for the 300 kVp, all diode detectors exhibited an over-responding behaviour compared to reference depth dose data measured with the Advanced Markus chamber. Relative output factors with the diodes were higher than the Advanced Markus chamber at low energy, and the magnitude of these differences is inversely proportional to the field sizes. The PTW P diode showed the highest variation of up to 15% in the output factor compared to the Advanced Markus chamber. CONCLUSION This study evaluated the dosimetric performance of a range of solid state detectors in kV relative dosimetry. This study showed that diode detectors are a suitable replacement for ionization chambers for the PDD measurement of low energy kV beams (60-150 kVp) except for the PDD of 60 kVp with the smaller field sizes. However, an over-responding behaviour of diode detectors at 300 kVp beams shows that diode detectors are not suitable for the PDD measurement of high energy kV beams. Generally, all solid state detectors over responded to ROF measurements, indicating that it is not suitable for ROF measurements. In general, both shielded and unshielded diodes produced a similar dosimetric response, which demonstrates that the energy dependence of solid state detectors should be considered before they are used for any kV relative dosimetric measurements. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- John Daniel
- North West Cancer Centre, Tamworth, NSW, Australia
| | | | | | - Robin Hill
- Department of Radiation Oncology, Chris O'Brien Lifehouse, Sydney, Australia.,Institute of Medical Physics, School of Physics, University of Sydney, Australia.,Biomedical Innovation, Chris O'Brien Lifehouse, Missenden Rd, Camperdown, Sydney, Australia
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Silvestre Patallo I, Carter R, Maughan D, Nisbet A, Schettino G, Subiel A. Evaluation of a micro ionization chamber for dosimetric measurements in image-guided preclinical irradiation platforms. Phys Med Biol 2021; 66. [PMID: 34794132 DOI: 10.1088/1361-6560/ac3b35] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2021] [Accepted: 11/18/2021] [Indexed: 11/12/2022]
Abstract
Image-guided small animal irradiation platforms deliver small radiation fields in the medium energy x-ray range. Commissioning of such platforms, followed by dosimetric verification of treatment planning, are mostly performed with radiochromic film. There is a need for independent measurement methods, traceable to primary standards, with the added advantage of immediacy in obtaining results. This investigation characterizes a small volume ionization chamber in medium energy x-rays for reference dosimetry in preclinical irradiation research platforms. The detector was exposed to a set of reference x-ray beams (0.5 to 4 mm Cu HVL). Leakage, reproducibility, linearity, response to detector's orientation, dose rate, and energy dependence were determined for a 3D PinPoint ionization chamber (PTW 31022). Polarity and ion recombination were also studied. Absorbed doses at 2 cm depth were compared, derived either by applying the experimentally determined cross-calibration coefficient at a typical small animal radiation platform "user's" quality (0.84 mm Cu HVL) or by interpolation from air kerma calibration coefficients in a set of reference beam qualities. In the range of reference x-ray beams, correction for ion recombination was less than 0.1%. The largest polarity correction was 1.4% (for 4 mm Cu HVL). Calibration and correction factors were experimentally determined. Measurements of absorbed dose with the PTW 31022, in conditions different from reference were successfully compared to measurements with a secondary standard ionization chamber. The implementation of an End-to-End test for delivery of image-targeted small field plans resulted in differences smaller than 3% between measured and treatment planning calculated doses. The investigation of the properties and response of a PTW 31022 small volume ionization chamber in medium energy x-rays and small fields can contribute to improve measurement uncertainties evaluation for reference and relative dosimetry of small fields delivered by preclinical irradiators while maintaining the traceability chain to primary standards.
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Affiliation(s)
- Ileana Silvestre Patallo
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Rebecca Carter
- Cancer Institute, University College London, London, London, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - David Maughan
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Andrew Nisbet
- Department of Medical Physics & Biomedical Engineering, University College London, London, London, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Giuseppe Schettino
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, Middlesex, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
| | - Anna Subiel
- Medical, Marine & Nuclear: Medical Radiation Physics&Sciences, National Physical Laboratory, Teddington, UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND
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Araki F. Determination of an ionization chamber response using quality index for kilovoltage x-ray beams. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2021.109595] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Real-time estimation of surface dose based on incident air kerma in diagnostic radiology. Phys Med 2021; 89:176-181. [PMID: 34388557 DOI: 10.1016/j.ejmp.2021.07.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/24/2021] [Revised: 07/14/2021] [Accepted: 07/28/2021] [Indexed: 11/20/2022] Open
Abstract
PURPOSE To estimate the surface dose in diagnostic radiology in real time based on the relationship between the incident air kerma and the surface dose. METHODS The air kerma for 20 X-ray beams with tube voltages of 50-140 kV and a half-value layer (HVL) of 2.27-9.65 mm Al was measured using an ionization chamber. The beam quality was classified based on the quality indexes (QIs) of 0.4, 0.5, and 0.6, which are defined as the ratio of the effective energy to the maximum energy corresponding to the tube potential. The surface dose for 20 X-ray beams was evaluated based on the measured air kerma, backscatter factor, and ratio of the mass-energy absorption coefficients of water to air, which were calculated using the Monte Carlo method. Finally, the relationship between the air kerma and the surface dose was investigated for X-ray beams with the specific QI values. RESULTS The surface dose at a water phantom was represented by a linear approximation of R2 > 0.98, with the air kerma, regardless of the X-ray beam quality. The surface dose estimated based on a linear approximation with the air kerma indicated an agreement within 8% with that evaluated by the chamber measurements at HVL > 3.4 mm Al. CONCLUSION It is possible to estimate the surface dose in real time using the linear relationship between the incident air kerma and the surface dose regardless of the X-ray beam quality by accepting ±10% uncertainty in the surface dose estimation.
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Massera RT, Fernández-Varea JM, Tomal A. Impact of photoelectric cross section data on systematic uncertainties for Monte Carlo breast dosimetry in mammography. Phys Med Biol 2021; 66. [PMID: 33857930 DOI: 10.1088/1361-6560/abf859] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Accepted: 04/15/2021] [Indexed: 11/11/2022]
Abstract
Monte Carlo (MC) simulations are employed extensively in breast dosimetry studies. In the energy interval of interest in mammography energy deposition is predominantly caused by the photoelectric effect, and the corresponding cross sections used by the MC codes to model this interaction process have a direct influence on the simulation results. The present work compares two photoelectric cross section databases in order to estimate the systematic uncertainty, related to breast dosimetry, introduced by the choice of cross sections for photoabsorption. The databases with and without the so-called normalization screening correction are denoted as 'renormalized' or 'un-normalized', respectively. The simulations were performed with the PENELOPE/penEasy code system, for a geometry resembling a mammography examination. The mean glandular dose (MGD), incident air kerma (Kair), normalized glandular dose (DgN) and glandular depth-dose (GDD(z)) were scored, for homogeneous breast phantoms, using both databases. The AAPM Report TG-195 case 3 was replicated, and the results were included. Moreover, cases with heterogeneous and anthropomorphic breast phantoms were also addressed. The results simulated with the un-normalized cross sections are in better overall agreement with the TG-195 data than those from the renormalized cross sections; for MGD the largest discrepancies are 0.13(6)% and 0.74(5)%, respectively. The MGD,Kairand DgN values simulated with the two databases show differences that diminish from approximately 10%/3%/6.8% at 8.25 keV down to 1.5%/1.7%/0.4% at 48.75 keV, respectively. For polyenergetic spectra, deviations up to 2.5% were observed. The disagreement between the GDDs simulated with the analyzed databases increases with depth, ranging from -1% near the breast entrance to 4% near the bottom. Thus, the choice of photoelectric cross section database affects the MC simulation results of breast dosimetry and adds a non-negligible systematic uncertainty to the dosimetric quantities used in mammography.
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Affiliation(s)
- Rodrigo T Massera
- Instituto de Física 'Gleb Wataghin', Universidade Estadual de Campinas, 13083-859, Campinas, Brazil
| | - José M Fernández-Varea
- Facultat de Física (FQA and ICC), Universitat de Barcelona, Diagonal 645, ES-08028 Barcelona, Catalonia, Spain
| | - Alessandra Tomal
- Instituto de Física 'Gleb Wataghin', Universidade Estadual de Campinas, 13083-859, Campinas, Brazil
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Valdes-Cortez C, Mansour I, Rivard MJ, Ballester F, Mainegra-Hing E, Thomson RM, Vijande J. A study of Type B uncertainties associated with the photoelectric effect in low-energy Monte Carlo simulations. Phys Med Biol 2021; 66. [PMID: 33662945 DOI: 10.1088/1361-6560/abebfd] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2021] [Accepted: 03/04/2021] [Indexed: 01/30/2023]
Abstract
Purpose.To estimate Type B uncertainties in absorbed-dose calculations arising from the different implementations in current state-of-the-art Monte Carlo (MC) codes of low-energy photon cross-sections (<200 keV).Methods.MC simulations are carried out using three codes widely used in the low-energy domain: PENELOPE-2018, EGSnrc, and MCNP. Three dosimetry-relevant quantities are considered: mass energy-absorption coefficients for water, air, graphite, and their respective ratios; absorbed dose; and photon-fluence spectra. The absorbed dose and the photon-fluence spectra are scored in a spherical water phantom of 15 cm radius. Benchmark simulations using similar cross-sections have been performed. The differences observed between these quantities when different cross-sections are considered are taken to be a good estimator for the corresponding Type B uncertainties.Results.A conservative Type B uncertainty for the absorbed dose (k = 2) of 1.2%-1.7% (<50 keV), 0.6%-1.2% (50-100 keV), and 0.3% (100-200 keV) is estimated. The photon-fluence spectrum does not present clinically relevant differences that merit considering additional Type B uncertainties except for energies below 25 keV, where a Type B uncertainty of 0.5% is obtained. Below 30 keV, mass energy-absorption coefficients show Type B uncertainties (k = 2) of about 1.5% (water and air), and 2% (graphite), diminishing in all materials for larger energies and reaching values about 1% (40-50 keV) and 0.5% (50-75 keV). With respect to their ratios, the only significant Type B uncertainties are observed in the case of the water-to-graphite ratio for energies below 30 keV, being about 0.7% (k = 2).Conclusions.In contrast with the intermediate (about 500 keV) or high (about 1 MeV) energy domains, Type B uncertainties due to the different cross-sections implementation cannot be considered subdominant with respect to Type A uncertainties or even to other sources of Type B uncertainties (tally volume averaging, manufacturing tolerances, etc). Therefore, the values reported here should be accommodated within the uncertainty budget in low-energy photon dosimetry studies.
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Affiliation(s)
- Christian Valdes-Cortez
- Departamento de Física Atómica, Molecular y Nuclear, Universitat de Valencia (UV), Burjassot, Spain.,Nuclear Medicine Department, Hospital Regional de Antofagasta, Chile
| | - Iymad Mansour
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, Canada
| | - Mark J Rivard
- Department of Radiation Oncology, Alpert Medical School of Brown University, Providence, RI, United States of America
| | - Facundo Ballester
- Departamento de Física Atómica, Molecular y Nuclear, Universitat de Valencia (UV), Burjassot, Spain.,Unidad Mixta de Investigación en Radiofísica e Instrumentación Nuclear en Medicina (IRIMED), Instituto de Investigación Sanitaria La Fe (IIS-La Fe)-Universitat de Valencia (UV), Valencia, Spain
| | | | - Rowan M Thomson
- Department of Physics, Carleton Laboratory for Radiotherapy Physics, Carleton University, Ottawa, Canada
| | - Javier Vijande
- Departamento de Física Atómica, Molecular y Nuclear, Universitat de Valencia (UV), Burjassot, Spain.,Unidad Mixta de Investigación en Radiofísica e Instrumentación Nuclear en Medicina (IRIMED), Instituto de Investigación Sanitaria La Fe (IIS-La Fe)-Universitat de Valencia (UV), Valencia, Spain.,Instituto de Física Corpuscular, IFIC (UV-CSIC), Burjassot, Spain
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Kilovoltage therapy is well and truly alive and needed in a modern radiotherapy centre. Phys Eng Sci Med 2021; 44:341-345. [PMID: 33899157 DOI: 10.1007/s13246-021-00998-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Araki F. Monte Carlo determination of a nanoDot OSLD response using quality index for diagnostic kilovoltage X-ray beams. Phys Med 2021; 84:101-108. [PMID: 33887616 DOI: 10.1016/j.ejmp.2021.03.031] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/17/2021] [Revised: 03/22/2021] [Accepted: 03/29/2021] [Indexed: 11/17/2022] Open
Abstract
PURPOSE This study aims to investigate the energy response of an optically stimulated luminescent dosimeter known as nanoDot for diagnostic kilovoltage X-ray beams via Monte Carlo calculations. METHODS The nanoDot response is calculated as a function of X-ray beam quality in free air and on a water phantom surface using Monte Carlo simulations. The X-ray fluence spectra are classified using the quality index (QI), which is defined as the ratio of the effective energy to the maximum energy of the photons. The response is calculated for X-ray fluence spectra with QIs of 0.4, 0.5, and 0.6 with tube voltages of 50-137.6 kVp and monoenergetic photon beams. The surface dose estimated using the calculated response is verified by comparing it with that measured using an ionization chamber. RESULTS The nanoDot response in free air for monoenergetic photon beams (QI = 1.0) varies significantly at photon energies below 100 keV and reaches a factor of 3.6 at 25-30 keV. The response differs by up to approximately 6% between QIs of 0.4 and 0.6 for the same half-value layer (HVL). The response at the phantom surface decreases slightly owing to the backscatter effect, and it is almost independent of the field size. The agreement between the surface dose estimated using the nanoDot and that measured using the ionization chamber for assessing X-ray beam qualities is less than 2%. CONCLUSIONS The nanoDot response is indicated as a function of HVL for the specified QIs, and it enables the direct surface dose measurement.
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Affiliation(s)
- Fujio Araki
- Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1 Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan.
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Nakatake C, Araki F. Energy response of radiophotoluminescent glass dosimeter for diagnostic kilovoltage x-ray beams. Phys Med 2021; 82:144-149. [PMID: 33611051 DOI: 10.1016/j.ejmp.2021.01.076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 01/12/2021] [Accepted: 01/24/2021] [Indexed: 10/22/2022] Open
Abstract
PURPOSE This study aimed to investigate the energy response of a radiophotoluminescent glass dosimeter (RGD) for diagnostic kilovoltage x-ray beams by Monte Carlo (MC) calculations and measurements. METHODS The uniformity and reproducibility of GD-352M (with Sn filter) and GD-302M (no filter) were tested with 45 RGDs in free air. Subsequently, the RGD response was obtained as a function of an Al-HVL using the parameter, quality index (QI), which is defined as the ratio of the effective energy (keV) to the maximum energy (keV) of the photons. The x-ray fluence spectra with QI of 0.4, 0.5, and 0.6 were set for tube voltages of 50 ~ 137.6 kVp. The RGD response was calculated in free air using the MC method and verified by the air kerma, Kair, measured using an ionization chamber. RESULTS The uniformity and reproducibility of the 45 RGDs were ± 2.3% and ± 2.7% for GD-352M and ± 0.7% and ± 1.6% for GD-302M at the one standard deviation level, respectively. The calculated RGD response was 0.965 to 1.062 at Al-HVL 2.73 mm or more for GD-352M and varied from 3.9 to 2.8 for GD-302M. Both RGD responses exhibited a good correlation with the Al-HVL for the given QI. Kair measured by RGDs for each beam quality with a QI of 0.5 was in the range of -5%~0.8% for GD-352M and -1.8%~3% for GD-302M, relative to the chamber measurements. CONCLUSIONS The RGD response was indicated as a function of the Al-HVL for the given QI, and it presented a good correlation with the Al-HVL.
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Affiliation(s)
- Chihiro Nakatake
- Graduate School of Health Sciences, Kumamoto University, 4-24-1, Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan
| | - Fujio Araki
- Department of Health Sciences, Faculty of Life Sciences, Kumamoto University, 4-24-1, Kuhonji, Chuo-ku, Kumamoto 862-0976, Japan.
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Chen Q, Zhang J. The impact of x-ray incident angle on indirect fluoroscopy skin dose estimation. Biomed Phys Eng Express 2021; 7:015005. [DOI: 10.1088/2057-1976/abc966] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Abstract
Indirect dosimetry to calculate peak skin dose (PSD) is generally based on reference air kerma or kerma-area-product, with effects of table attenuation, inverse square law and backscatter factor applied. When the incident x-ray beam angle changes, these factors would change as well. The purpose of this study is to identify the impact of incident x-ray beam angle on the accuracy of indirect PSD calculation and develop a correction method. Monte Carlo simulation was conducted to assist analytical equation derivation and to validate the developed analytical method. Direct PSD measurements were performed a Siemens Artis Zee biplane fluoroscopy and a GE OEC C-Arm at different angles to validate the proposed correction method and its independence of fluoroscopy systems. Compared with MC simulated PSD, the derived analytical equation successfully predicts these PSD changes for incident angles of 0, 15, 30 and 40 degrees, with the residual error magnitude of 0.3%–3.1% corresponding to different SSDs. The agreement between calculated PSD also agrees well with direct measurement.
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Czarnecki D, Zink K, Pimpinella M, Borbinha J, Teles P, Pinto M. Monte Carlo calculation of quality correction factors based on air kerma and absorbed dose to water in medium energy x-ray beams. Phys Med Biol 2020; 65:245042. [PMID: 33120372 DOI: 10.1088/1361-6560/abc5c9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Clinical dosimetry is typically performed using ion chambers calibrated in terms of absorbed dose to water. As primary measurement standards for this quantity for low and medium energy x-rays are available only since a few years, most dosimetry protocols for this photon energy range are still based on air kerma calibration. For that reason, data for beam quality correction factors [Formula: see text], necessary for the application of dose to water based protocols, are scarce in literature. Currently the international IAEA TRS-398 Code of Practice is under revision and new [Formula: see text] factors for a large number of ion chambers will be introduced in the update of this protocol. Several international groups provided the IAEA with experimental and Monte Carlo based data for this revision. Within the European Community the EURAMET 16NRM03 RTNORM project was initiated for that purpose. In the present study, Monte Carlo based results for the beam quality correction factors in medium energy x-ray beams for six ion chambers applying different Monte Carlo codes are presented. Additionally, the perturbation factor p Q , necessary for the calculation of dose to water from an air kerma calibration coefficient, was determined. The beam quality correction factor [Formula: see text] for the chambers varied in the investigated energy range by about 4%-5%, and for five out of six chambers the data could be fitted by a simple logarithmic function, if the half-value-layer was used as the beam quality specifier. Corresponding data using different Monte Carlo codes for the same ion chamber agreed within 0.5%. For the perturbation factor p Q , the data did not obey a comparable simple relationship with the beam quality specifier. The variation of p Q for all ion chambers was in the range of 3%-4%. Compared to recently published data, our p Q data is around 1% larger, although the same Monte Carlo code has been used. Compared to the latest experimental data, there are even deviations in the range of 2%.
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Affiliation(s)
- Damian Czarnecki
- Institute of Medical Physics and Radiation Protection, University of Applied Sciences Giessen (THM), Giessen, Germany
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Valdes-Cortez C, Ballester F, Vijande J, Gimenez V, Gimenez-Alventosa V, Perez-Calatayud J, Niatsetski Y, Andreo P. Depth-dose measurement corrections for the surface electronic brachytherapy beams of an Esteya ® unit: a Monte Carlo study. Phys Med Biol 2020; 65. [DOI: 10.1088/1361-6560/ab9773] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 05/28/2020] [Indexed: 11/12/2022]
Abstract
Abstract
Three different correction factors for measurements with the parallel-plate ionization chamber PTW T34013 on the Esteya electronic brachytherapy unit have been investigated. This chamber type is recommended by AAPM TG-253 for depth-dose measurements in the 69.5 kV x-ray beam generated by the Esteya unit.
Monte Carlo simulations using the PENELOPE-2018 system were performed to determine the absorbed dose deposited in water and in the chamber sensitive volume at different depths with a Type A uncertainty smaller than 0.1%. Chamber-to-chamber differences have been explored performing measurements using three different chambers. The range of conical applicators available, from 10 to 30 mm in diameter, has been explored.
Using a depth-independent global chamber perturbation correction factor without a shift of the effective point of measurement yielded differences between the absorbed dose to water and the corrected absorbed dose in the sensitive volume of the chamber of up to 1% and 0.6% for the 10 mm and 30 mm applicators, respectively. Calculations using a depth-dependent perturbation factor, including or excluding a shift of the effective point of measurement, resulted in depth-dose differences of about ± 0.5% or less for both applicators. The smallest depth-dose differences were obtained when a shift of the effective point of measurement was implemented, being displaced 0.4 mm towards the center of the sensitive volume of the chamber. The correction factors were obtained with combined uncertainties of 0.4% (k = 2). Uncertainties due to chamber-to-chamber differences are found to be lower than 2%.
The results emphasize the relevance of carrying out detailed Monte Carlo studies for each electronic brachytherapy device and ionization chamber used for its dosimetry.
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Wang XJ, Miguel B, Seuntjens J, Fernández-Varea JM. On the relativistic impulse approximation for the calculation of Compton scattering cross sections and photon interaction coefficients used in kV dosimetry. ACTA ACUST UNITED AC 2020; 65:125010. [DOI: 10.1088/1361-6560/ab8108] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Bancheri J, Ketelhut S, Büermann L, Seuntjens J. Monte Carlo and water calorimetric determination of kilovoltage beam radiotherapy ionization chamber correction factors. ACTA ACUST UNITED AC 2020; 65:105001. [DOI: 10.1088/1361-6560/ab82e7] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Andreo P, Burns DT, Kapsch RP, McEwen M, Vatnitsky S, Andersen CE, Ballester F, Borbinha J, Delaunay F, Francescon P, Hanlon MD, Mirzakhanian L, Muir B, Ojala J, Oliver CP, Pimpinella M, Pinto M, de Prez LA, Seuntjens J, Sommier L, Teles P, Tikkanen J, Vijande J, Zink K. Determination of consensus k Q values for megavoltage photon beams for the update of IAEA TRS-398. ACTA ACUST UNITED AC 2020; 65:095011. [DOI: 10.1088/1361-6560/ab807b] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Subiel A, Silvestre Patallo I, Palmans H, Barry M, Tulk A, Soultanidis G, Greenman J, Green VL, Cawthorne C, Schettino G. The influence of lack of reference conditions on dosimetry in pre-clinical radiotherapy with medium energy x-ray beams. Phys Med Biol 2020; 65:085016. [PMID: 32109893 DOI: 10.1088/1361-6560/ab7b30] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Despite well-established dosimetry in clinical radiotherapy, dose measurements in pre-clinical and radiobiology studies are frequently inadequate, thus undermining the reliability and reproducibility of published findings. The lack of suitable dosimetry protocols, coupled with the increasing complexity of pre-clinical irradiation platforms, undermines confidence in preclinical studies and represents a serious obstacle in the translation to clinical practice. To accurately measure output of a pre-clinical radiotherapy unit, appropriate Codes of Practice (CoP) for medium energy x-rays needs to be employed. However, determination of absorbed dose to water (Dw) relies on application of backscatter factor (Bw) employing in-air method or carrying out in-phantom measurement at the reference depth of 2 cm in a full backscatter (i.e. 30 × 30 × 30 cm3) condition. Both of these methods require thickness of at least 30 cm of underlying material, which are never fulfilled in typical pre-clinical irradiations. This work is focused on evaluation the effects of the lack of recommended reference conditions in dosimetry measurements for pre-clinical settings and is aimed at extending the recommendations of the current CoP to practical experimental conditions and highlighting the potential impact of the lack of correct backscatter considerations on radiobiological studies.
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Affiliation(s)
- Anna Subiel
- National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW, United Kingdom. Author to whom any correspondence should be addressed
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Valdes-Cortez C, Niatsetski Y, Ballester F, Vijande J, Candela-Juan C, Perez-Calatayud J. On the use of the absorbed depth-dose measurements in the beam calibration of a surface electronic high-dose-rate brachytherapy unit, a Monte Carlo-based study. Med Phys 2019; 47:693-702. [PMID: 31722113 DOI: 10.1002/mp.13920] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 11/06/2019] [Accepted: 11/06/2019] [Indexed: 01/25/2023] Open
Abstract
PURPOSE To evaluate the use of the absorbed depth-dose as a surrogate of the half-value layer in the calibration of a high-dose-rate electronic brachytherapy (eBT) equipment. The effect of the manufacturing tolerances and the absorbed depth-dose measurement uncertainties in the calibration process are also addressed. METHODS The eBT system Esteya® (Elekta Brachytherapy, Veenendaal, The Netherlands) has been chosen as a proof-of-concept to illustrate the feasibility of the proposed method, using its 10 mm diameter applicator. Two calibration protocols recommended by the AAPM (TG-61) and the IAEA (TRS-398) for low-energy photon beams were evaluated. The required Monte Carlo (MC) simulations were carried out using PENELOPE2014. Several MC simulations were performed modifying the flattening filter thickness and the x-ray tube potential, generating one absorbed depth-dose curve and a complete set of parameters required in the beam calibration (i.e., HVL, backscatter factor (Bw ), and mass energy-absorption coefficient ratios (µen /ρ)water,air ), for each configuration. Fits between each parameter and some absorbed dose-ratios calculated from the absorbed depth-dose curves were established. The effect of the manufacturing tolerances and the absorbed dose-ratio uncertainties over the calibration process were evaluated by propagating their values over the fitting function, comparing the overall calibration uncertainties against reference values. We proposed four scenarios of uncertainty (from 0% to 10%) in the dose-ratio determination to evaluate its effect in the calibration process. RESULTS The manufacturing tolerance of the flattening filter (±0.035 mm) produces a change of 1.4% in the calculated HVL and a negligible effect over the Bw , (µen /ρ)water,air , and the overall calibration uncertainty. A potential variation of 14% of the electron energies due to manufacturing tolerances in the x-ray tube (69.5 ± ~10 keV) generates a variation of 10% in the HVL. However, this change has a negligible effect over the Bw and (µen /ρ)water,air , adding 0.1% to the overall calibration uncertainty. The fitting functions reproduce the data with an uncertainty (k = 2) below 1%, 0.5%, and 0.4% for the HVL, Bw , and (µen /ρ)water,air , respectively. The four studied absorbed dose-ratio uncertainty scenarios add, in the worst-case scenario, 0.2% to the overall uncertainty of the calibration process. CONCLUSIONS This work shows the feasibility of using the absorbed depth-dose curve in the calibration of an eBT system with minimal loss of precision.
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Affiliation(s)
- Christian Valdes-Cortez
- Departamento de Física Atómica, Molecular y Nuclear, Universidad de Valencia (UV), Valencia, 46100, Spain.,Radiotherapy Department, Centro Oncológico del Norte, Antofagasta, 1240000, Chile
| | - Yury Niatsetski
- R&D Elekta Brachytherapy, Waardgelder 1, 3905 TH, Veenendaal, The Netherlands
| | - Facundo Ballester
- Departamento de Física Atómica, Molecular y Nuclear, Universidad de Valencia (UV), Valencia, 46100, Spain.,IRIMED Joint Research Unit (IIS La Fe - UV), Valencia, Spain
| | - Javier Vijande
- Departamento de Física Atómica, Molecular y Nuclear, Universidad de Valencia (UV), Valencia, 46100, Spain.,IRIMED Joint Research Unit (IIS La Fe - UV), Valencia, Spain
| | - Cristian Candela-Juan
- Centro Nacional de Dosimetría (CND), Instituto Nacional de Gestión Sanitaria, Valencia, 46009, Spain
| | - Jose Perez-Calatayud
- IRIMED Joint Research Unit (IIS La Fe - UV), Valencia, Spain.,Radiotherapy Department, La Fe Hospital, Valencia, 46026, Spain
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