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Walter AE, DeWerd LA. Feasibility of implementing a megavoltage ionization chamber calibration service at the secondary standards level. Radiat Phys Chem Oxf Engl 1993 2022. [DOI: 10.1016/j.radphyschem.2022.110699] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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2
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Khan AU, Simiele EA, DeWerd LA. Monte Carlo-derived ionization chamber correction factors in therapeutic carbon ion beams. Phys Med Biol 2021; 66. [PMID: 34464949 DOI: 10.1088/1361-6560/ac226c] [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: 05/09/2021] [Accepted: 08/31/2021] [Indexed: 11/12/2022]
Abstract
The accuracy of electromagnetic transport in the GEANT4 Monte Carlo (MC) code was investigated for carbon ion beams and ionization chamber (IC)-specific beam quality correction factors were calculated. This work implemented a Fano cavity test for carbon ion beams in the 100-450 MeV/u energy range to assess the accuracy of the default electromagnetic physics parameters. TheUrbanand theWentzel-VImultiple Coulomb scattering models were evaluated and the impact ofmaxStep,dRover,andfinal rangeparameters on the accuracy of the transport algorithm was investigated. The optimal production thresholds for an accurate calculation offQvalues, which is the product of the water-to-air stopping power ratio and the IC-specific perturbation correction factor, were also studied. ThefQcorrection factors were calculated for a cylindrical and a parallel-plate IC using carbon ions in the 150-450 MeV/u energy range. Modifying the default electromagnetic physics parameters resulted in a maximum deviation from theory of 0.3%. Therefore, the default EM parameters were used for the remainder of this work. ThefQfactors were found to converge for both ICs with decreasing production threshold distance below 5μm. ThefQvalues obtained in this work agreed with the TRS-398 stopping power ratios and other previously reported results within uncertainty. This study highlights an accurate MC-based technique to calculate the combined stopping power ratio and the perturbation correction factor for any IC in carbon ion beams.
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Affiliation(s)
- Ahtesham Ullah Khan
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, United States of America
| | - Eric A Simiele
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, United States of America
| | - Larry A DeWerd
- Department of Medical Physics, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, WI 53705, United States of America
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Lam S, Bradley D, Khandaker M. Small-field radiotherapy photon beam output evaluation: Detectors reviewed. Radiat Phys Chem Oxf Engl 1993 2021. [DOI: 10.1016/j.radphyschem.2020.108950] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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4
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Reis C, Nicolucci P. Assessment of ionization chamber correction factors in photon beams using a time saving strategy with PENELOPE code. Phys Med 2016; 32:297-304. [DOI: 10.1016/j.ejmp.2016.01.482] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/07/2015] [Revised: 01/20/2016] [Accepted: 01/22/2016] [Indexed: 10/22/2022] Open
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Krauss A, Kapsch RP. Experimental determination ofkQfactors for cylindrical ionization chambers in 10 cm × 10 cm and 3 cm × 3 cm photon beams from 4 MV to 25 MV. Phys Med Biol 2014; 59:4227-46. [DOI: 10.1088/0031-9155/59/15/4227] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Andreo P, Wulff J, Burns DT, Palmans H. Consistency in reference radiotherapy dosimetry: resolution of an apparent conundrum when60Co is the reference quality for charged-particle and photon beams. Phys Med Biol 2013; 58:6593-621. [DOI: 10.1088/0031-9155/58/19/6593] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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7
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Lye JE, Butler DJ, Ramanathan G, Franich RD. Spectral differences in 6 MV beams with matched PDDs and the effect on chamber response. Phys Med Biol 2012; 57:7599-614. [DOI: 10.1088/0031-9155/57/22/7599] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Moussous O, Khoudri S, Benguerba M. Characterization of a Fricke dosimeter at high energy photon and electron beams used in radiotherapy. AUSTRALASIAN PHYSICAL & ENGINEERING SCIENCES IN MEDICINE 2011; 34:523-8. [DOI: 10.1007/s13246-011-0093-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 08/02/2011] [Indexed: 11/25/2022]
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9
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Wulff J, Heverhagen JT, Zink K, Kawrakow I. Investigation of systematic uncertainties in Monte Carlo-calculated beam quality correction factors. Phys Med Biol 2010; 55:4481-93. [DOI: 10.1088/0031-9155/55/16/s04] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Abdel-Rahman W, Evans MDC, Serré L, McCaffrey JP, Podgorsak EB, Seuntjens JP. Clinic based transfer of the ND,wC60o calibration coefficient using a linear accelerator. Med Phys 2009; 36:929-38. [DOI: 10.1118/1.3075822] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Castrillón SV, Henríquez FC. Comparison of IPSM 1990 photon dosimetry code of practice with IAEA TRS-398 and AAPM TG-51. J Appl Clin Med Phys 2009; 10:136-146. [PMID: 19223831 PMCID: PMC5720500 DOI: 10.1120/jacmp.v10i1.2810] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2008] [Accepted: 09/02/2008] [Indexed: 11/24/2022] Open
Abstract
Several codes of practice for photon dosimetry are currently used around the world, supported by different organizations. A comparison of IPSM 1990 with both IAEA TRS-398 and AAPM TG-51 has been performed. All three protocols are based on the calibration of ionization chambers in terms of standards of absorbed dose to water, as it is the case with other modern codes of practice. This comparison has been carried out for photon beams of nominal energies: 4 MV, 6 MV, 8 MV, 10 MV and 18 MV. An NE 2571 graphite ionization chamber was used in this study, cross-calibrated against an NE 2611A Secondary Standard, calibrated in the National Physical Laboratory (NPL). Absolute dose in reference conditions was obtained using each of these three protocols including: beam quality indices, beam quality conversion factors both theoretical and NPL experimental ones, correction factors for influence quantities and absolute dose measurements. Each protocol recommendations have been strictly followed. Uncertainties have been obtained according to the ISO Guide to the Expression of Uncertainty in Measurement. Absorbed dose obtained according to all three protocols agree within experimental uncertainty. The largest difference between absolute dose results for two protocols is obtained for the highest energy: 0.7% between IPSM 1990 and IAEA TRS-398 using theoretical beam quality conversion factors.
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Wulff J, Heverhagen JT, Zink K. Monte-Carlo-based perturbation and beam quality correction factors for thimble ionization chambers in high-energy photon beams. Phys Med Biol 2008; 53:2823-36. [DOI: 10.1088/0031-9155/53/11/005] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Austerlitz C, Mota H, Almeida CE, Allison R, Sibata C. Quality assurance of HDR 192Ir sources using a Fricke dosimeter. Med Phys 2007; 34:1348-53. [PMID: 17500465 DOI: 10.1118/1.2714472] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
A prototype of a Fricke dosimetry system consisting of a 15 x 15 x 15 cm3 water phantom made of Plexiglas and a 11.3-ml Pyrex balloon fitted with a 0.2 cm thick Pyrex sleeve in its center was created to assess source strength and treatment planning algorithms for use in high dose rate (HDR) 192Ir afterloading units. In routine operation, the radioactive source is positioned at the end of a sleeve, which coincides with the center of the spherical balloon that is filled with Fricke solution, so that the solution is nearly isotropically irradiated. The Fricke system was calibrated in terms of source strength against a reference well-type ionization chamber, and in terms of radial dose by means of an existing algorithm from the HDR's treatment planning system. Because the system is based on the Fricke dosimeter itself, for a given type and model of 192Ir source, the system needs initial calibration but no recalibration. The results from measurements made over a 10 month period, including source decay and source substitutions, have shown the feasibility of using such a system for quality control (QC) of HDR afterloading equipment, including both the source activity and treatment planning parameters. The benefit of a large scale production and the use of this device for clinical HDR QC audits via mail are also discussed.
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Affiliation(s)
- C Austerlitz
- The Brody School of Medicine, East Carolina University, Department of Radiation Oncology, 600 Moye Boulevard, Greenville, North Carolina 27858, USA
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Huq MS, Andreo P. Advances in the determination of absorbed dose to water in clinical high-energy photon and electron beams using ionization chambers. Phys Med Biol 2004; 49:R49-104. [PMID: 15005158 DOI: 10.1088/0031-9155/49/4/r01] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
During the last two decades, absorbed dose to water in clinical photon and electron beams was determined using dosimetry protocols and codes of practice based on radiation metrology standards of air kerma. It is now recommended that clinical reference dosimetry be based on standards of absorbed dose to water. Newer protocols for the dosimetry of radiotherapy beams, based on the use of an ionization chamber calibrated in terms of absorbed dose to water, N(D,w), in a standards laboratory's reference quality beam, have been published by several national or regional scientific societies and international organizations. Since the publication of these protocols multiple theoretical and experimental dosimetry comparisons between the various N(D,w) based recommendations, and between the N(D,w) and the former air kerma (NK) based protocols, have been published. This paper provides a comprehensive review of the dosimetry protocols based on these standards and of the intercomparisons of the different protocols published in the literature, discussing the reasons for the observed discrepancies between them. A summary of the various types of standards of absorbed dose to water, together with an analysis of the uncertainties along the various steps of the dosimetry chain for the two types of formalism, is also included. It is emphasized that the NK-N(D,air) and N(D,w) formalisms have very similar uncertainty when the same criteria are used for both procedures. Arguments are provided in support of the recommendation for a change in reference dosimetry based on standards of absorbed dose to water.
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Affiliation(s)
- M Saiful Huq
- Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA
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Lopez Medina A, Teijeiro A, Salvador F, Medal D, Vazquez J, Salgado M, Carrion MC. Comparison between TG-51 and TRS-398: electron contamination effect on photon beam-quality specification. Phys Med Biol 2003; 49:17-32. [PMID: 14971770 DOI: 10.1088/0031-9155/49/1/002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Two dosimetry protocols based on absorbed dose to water have recently been implemented: TG-51 and TRS-398. These protocols use different beam-quality indices: %dd(10)x and TPR20,10. The effect of electron contamination in measurements of %dd(10)x has been proposed as a disadvantage of the TG-51. For actual measurements of %dd(10)x in five clinical beams (Primus 6-18 MV, SL-75/5 6 MV, SL-18 6-15 MV) a purging magnet was employed to remove the electron contamination. Also, %dd(10)x was measured in the different ways described in TG-51 for high-energy beams: with a lead foil at 50 cm from the phantom surface, at 30 cm, and for open beam. Moreover, TPR20,10 was determined. Also, periodic quality-control measurements were used for comparing both quality indices and variation over time, but D20,10 was used instead of TPR20,10 and measurements in open beam for the %dd(10)x determination. Considering both protocols, S(w,air) and kQ were calculated in order to compare the results with the experimental data. Significant differences (0.3% for kQ) were only found for the two high-energy beams, but when the electron contamination is underestimated by TG-51, the difference in kQ is lower. Differences in the other cases and variations over time were less than 0.1%.
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Affiliation(s)
- Antonio Lopez Medina
- Department of Medical Physics, Instituto Galego de Medicina Tecnica, Hospital do Meixoeiro, 36200 Vigo, Spain.
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Palm A, Mattsson O. Experimental determination of beam quality conversion factors k(Q) in clinical photon beams using ferrous sulphate (Fricke) dosimetry. Med Phys 2002; 29:2756-62. [PMID: 12512708 DOI: 10.1118/1.1521941] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
The implementation of protocols based on absorbed dose to water standards requires beam quality conversion factors, k(Q). Calculated values of k(Q) are available for ionization chambers used for reference dosimetry. Ideally, k(Q) should be experimentally determined at the same beam qualities as that of the user. In this work we measure k(Q) factors in clinical photon beams and compare them with calculated and measured values. Beam quality conversion factors are determined for clinical photon beams of nominal energies 4 MV, 6 MV, 15 MV, and 25 MV, for commonly used cylindrical ionization chambers. Twelve chambers of eight different types are used. For three of them, no experimental data have previously been available. The experimental procedure is based on measurements with ionization chambers and Fricke dosimetry in the reference beam (60Co gamma radiation) and in clinical linear accelerator beams. The k(Q) values determined in this work generally agree within 0.5% with previously reported experimental values both when %dd(10)x and TPR2010 are used for beam quality specification. The agreement with calculated data is generally within 0.5%, except for the 15 MV beam. For this beam the measured values are usually between 0.5% and 1% lower than the data taken from the TG-51 protocol or the TRS-398 code of practice. For three NE2571 chambers and three NE2581 chambers, the maximum observed deviation of individual k(Q) values is 0.2% and 0.4%, respectively.
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Affiliation(s)
- Asa Palm
- Department of Radiation Physics, Sahlgrenska University Hospital, SE413 45 Göteborg, Sweden.
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Andreo P, Huq MS, Westermark M, Song H, Tilikidis A, DeWerd L, Shortt K. Protocols for the dosimetry of high-energy photon and electron beams: a comparison of the IAEA TRS-398 and previous international codes of practice. International Atomic Energy Agency. Phys Med Biol 2002; 47:3033-53. [PMID: 12361209 DOI: 10.1088/0031-9155/47/17/301] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A new international Code of Practice for radiotherapy dosimetry co-sponsored by several international organizations has been published by the IAEA, TRS-398. It is based on standards of absorbed dose to water, whereas previous protocols (TRS-381 and TRS-277) were based on air kerma standards. To estimate the changes in beam calibration caused by the introduction of TRS-398, a detailed experimental comparison of the dose determination in reference conditions in high-energy photon and electron beams has been made using the different IAEA protocols. A summary of the formulation and reference conditions in the various Codes of Practice, as well as of their basic data, is presented first. Accurate measurements have been made in 25 photon and electron beams from 10 clinical accelerators using 12 different cylindrical and plane-parallel chambers, and dose ratios under different conditions of TRS-398 to the other protocols determined. A strict step-by-step checklist was followed by the two participating clinical institutions to ascertain that the resulting calculations agreed within tenths of a per cent. The maximum differences found between TRS-398 and the previous Codes of Practice TRS-277 (2nd edn) and TRS-381 are of the order of 1.5-2.0%. TRS-398 yields absorbed doses larger than the previous protocols, around 1.0% for photons (TRS-277) and for electrons (TRS-381 and TRS-277) when plane-parallel chambers are cross-calibrated. For the Markus chamber, results show a very large variation, although a fortuitous cancellation of the old stopping powers with the ND,w/NK ratios makes the overall discrepancy between TRS-398 and TRS-277 in this case smaller than for well-guarded plane-parallel chambers. Chambers of the Roos-type with a 60Co ND,w calibration yield the maximum discrepancy in absorbed dose, which varies between 1.0% and 1.5% for TRS-381 and between 1.5% and 2.0% for TRS-277. Photon beam calibrations using directly measured or calculated TPR20,10 from a percentage dose data at SSD = 100 cm were found to be indistinguishable. Considering that approximately 0.8% of the differences between TRS-398 and the NK-based protocols are caused by the change to the new type of standards, the remaining difference in absolute dose is due either to a close similarity in basic data or to a fortuitous cancellation of the discrepancies in data and type of chamber calibration. It is emphasized that the NK-ND,air and ND,w formalisms have very similar uncertainty when the same criteria are used for both procedures. Arguments are provided in support of the recommendation for a change in reference dosimetry based on standards of absorbed dose to water.
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Affiliation(s)
- Pedro Andreo
- Division of Medical Radiation Physics, University of Stockholm, Karolinska Institute, Sweden
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18
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Thierens HPWMAH. Beam quality of high-energy photon beams at the Ghent University linear accelerator. Phys Med Biol 2002. [DOI: 10.1088/0031-9155/47/17/101] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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19
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Palmans H, Nafaa L, De JJ, Gillis S, Hoornaert MT, Martens C, Piessens M, Thierens H, Van der Plaetsen A, Vynckier S. Absorbed dose to water based dosimetry versus air kerma based dosimetry for high-energy photon beams: an experimental study. Phys Med Biol 2002; 47:421-40. [PMID: 11848121 DOI: 10.1088/0031-9155/47/3/305] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In recent years, a change has been proposed from air kerma based reference dosimetry to absorbed dose based reference dosimetry for all radiotherapy beams of ionizing radiation. In this paper, a dosimetry study is presented in which absorbed dose based dosimetry using recently developed formalisms was compared with air kerma based dosimetry using older formalisms. Three ionization chambers of each of three different types were calibrated in terms of absorbed dose to water and air kerma and sent to five hospitals. There, reference dosimetry with all the chambers was performed in a total of eight high-energy clinical photon beams. The selected chamber types were the NE2571, the PTW-30004 and the Wellhöfer-FC65G (previously Wellhöfer-IC70). Having a graphite wall, they exhibit a stable volume and the presence of an aluminium electrode ensures the robustness of these chambers. The data were analysed with the most important recommendations for clinical dosimetry: IAEA TRS-398, AAPM TG-51, IAEA TRS-277, NCS report-2 (presently recommended in Belgium) and AAPM TG-21. The necessary conversion factors were taken from those protocols, or calculated using the data in the different protocols if data for a chamber type are lacking. Polarity corrections were within 0.1% for all chambers in all beams. Recombination corrections were consistent with theoretical predictions, did not vary within a chamber type and only slightly between different chamber types. The maximum chamber-to-chamber variations of the dose obtained with the different formalisms within the same chamber type were between 0.2% and 0.6% for the NE2571, between 0.2% and 0.6% for the PTW-30004 and 0.1% and 0.3% for the Wellhöfer-FC65G for the different beams. The absorbed dose results for the NE2571 and Wellhöfer-FC65G chambers were in good agreement for all beams and all formalisms. The PTW-30004 chambers gave a small but systematically higher result compared to the result for the NE2571 chambers (on the average 0.1% for IAEA TRS-277, 0.3% for NCS report-2 and AAPM TG-21 and 0.4% for IAEA TRS-398 and AAPM TG-51). Within the air kerma based protocols, the results obtained with the TG-21 protocol were 0.4-0.8% higher mainly due to the differences in the data used. Both absorbed dose to water based formalisms resulted in consistent values within 0.3%. The change from old to new formalisms is discussed together with the traceability of calibration factors obtained at the primary absorbed dose and air kerma standards in the reference beams (60Co). For the particular situation in Belgium (calibrations at the Laboratory for Standard Dosimetry of Ghent) the change amounts to 0.1-0.6%. This is similar to the magnitude of the change determined in other countries.
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Affiliation(s)
- Hugo Palmans
- Subatomic and Radiation Physics Department, Ghent University, Gent, Belgium.
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Boas JF, Huntley RB, Webb DV. The relative response of NE2561 and NE2611A ionization chambers in megavoltage x-ray beams. Phys Med Biol 2001; 46:3259-67. [PMID: 11768504 DOI: 10.1088/0031-9155/46/12/313] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The relative energy response of NE2561 and NE261 IA ionization chambers to megavoltage photon beams from the ARPANSA linac indicates significant differences between these two types of chamber. In 16 MV beams of TPR20(10) 0.779, differences of about 2% are observed. The results are expressed as ratios KQ of the beam quality correction factors kQ, where the kQ factor for each type of chamber is the ratio of the absorbed dose to water calibration factor ND, at the x-ray quality Q to that at 60Co. These results have implications for the use of generic kQ factors in dosimetry protocols and suggest that NE2561 and NE2611A ionization chambers cannot be assumed to be identical.
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Affiliation(s)
- J F Boas
- Australian Radiation Protection and Nuclear Safety Agency, Yallambie, Victoria
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Huq MS, Andreo P, Song H. Comparison of the IAEA TRS-398 and AAPM TG-51 absorbed dose to water protocols in the dosimetry of high-energy photon and electron beams. Phys Med Biol 2001; 46:2985-3006. [PMID: 11720359 DOI: 10.1088/0031-9155/46/11/315] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The International Atomic Energy Agency (IAEA TRS-398) and the American Association of Physicists in Medicine (AAPM TG-51) have published new protocols for the calibration of radiotherapy beams. These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standards laboratory's reference quality beam. This paper compares the recommendations of the two protocols in two ways: (i) by analysing in detail the differences in the basic data included in the two protocols for photon and electron beam dosimetry and (ii) by performing measurements in clinical photon and electron beams and determining the absorbed dose to water following the recommendations of the two protocols. Measurements were made with two Farmer-type ionization chambers and three plane-parallel ionization chamber types in 6, 18 and 25 MV photon beams and 6, 8, 10, 12, 15 and 18 MeV electron beams. The Farmer-type chambers used were NE 2571 and PTW 30001, and the plane-parallel chambers were a Scanditronix-Wellhöfer NACP and Roos, and a PTW Markus chamber. For photon beams, the measured ratios TG-51/TRS-398 of absorbed dose to water Dw ranged between 0.997 and 1.001, with a mean value of 0.999. The ratios for the beam quality correction factors kQ were found to agree to within about +/-0.2% despite significant differences in the method of beam quality specification for photon beams and in the basic data entering into kQ. For electron beams, dose measurements were made using direct N(D,w) calibrations of cylindrical and plane-parallel chambers in a 60Co gamma-ray beam, as well as cross-calibrations of plane-parallel chambers in a high-energy electron beam. For the direct N(D,w) calibrations the ratios TG-51/TRS-398 of absorbed dose to water Dw were found to lie between 0.994 and 1.018 depending upon the chamber and electron beam energy used, with mean values of 0.996, 1.006, and 1.017, respectively, for the cylindrical, well-guarded and not well-guarded plane-parallel chambers. The Dw ratios measured for the cross-calibration procedures varied between 0.993 and 0.997. The largest discrepancies for electron beams between the two protocols arise from the use of different data for the perturbation correction factors p(wall) and p(dis) of cylindrical and plane-parallel chambers, all in 60Co. A detailed analysis of the reasons for the discrepancies is made which includes comparing the formalisms, correction factors and the quantities in the two protocols.
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Affiliation(s)
- M S Huq
- Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA
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22
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Bielajew AF. Commentary: the controversy between the IAEA Code of Practice and the TG-51 protocol. Phys Med Biol 2000; 45:2 p following table of contents. [PMID: 11008944 DOI: 10.1088/0031-9155/45/9/001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- A F Bielajew
- The University of Michigan, Ann Arbor 48109-2104, USA.
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