Direct measurement of ionization chamber absorbed dose k factors in clinical electron beams

Wang, Zhipeng; Xing, Shuming; Wang, Kun; Jin, Sunjun; Zhang, Jian; Fan, Fuyou

doi:10.1016/j.radmeas.2020.106481

Cited by 6 publications

(5 citation statements)

References 21 publications

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“…For high energy photon beams, the measurements by Seuntjens et al 15 and McEwen 16 have not only provided numerical data to back up the theoretical k Q data adopted in the current protocols 11,12 but also added experimental k Q data for a wide range of thimble chambers. For electron beams, the experimental studies by Renaud et al, 17 Muir et al, 18 Krauss and Kapsch, 19 and Wang et al 20 have provided k Q data that are also in good agreement with what are adopted in the current protocols. 11,12 The beam quality conversion factor, k Q , can also be calculated directly for specific chambers using Monte Carlo simulations.…”

Section: Introductionsupporting

confidence: 54%

Stopping‐power ratios for electron beams used in total skin electron therapy

Ding

2021

Medical Physics

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Purpose The electron beams for total skin electron therapy (TSET) are often degraded by a scatter plate in addition to extended distances. For electron dosimetry, both the AAPM TG‐51 and IAEA TRS‐398 recommend the use of two formulas developed by Burns et al [Med. Phys. 23, 489–501 (1996)] to estimate the water‐to‐air stopping‐power ratios (SPRs). Both formulas are based on a fit to SPRs calculated for standard electron beams. This study aims to find: (1) if the formulas are applicable to beams used in TSET and (2) the impact of the ICRU report 90 recommendations on the SPRs for these beams. Methods The EGSnrc Monte Carlo code system is used to generate 6 MeV high dose rate total skin electron (HDTSe) beams used in TSET. The simulated beams are used to calculate dose distributions and SPRs as a function of depth in a water phantom. The fitted SPRs using the empirical formulas are compared with MC‐calculated SPRs. Results The electron beam quality specifier, the depth in water at which the absorbed dose falls to 50% of its maximum value, R50, decreases approximately 1 mm for each additional 100‐cm extended distance ranging from 2.24 cm at SSD = 100 to 1.72 cm at SSD = 700 cm. For beams passing through a scatter plate, R50 is 1.76 cm (1.14) at SSD = 300 and 1.48 cm (0.85 cm) at SSD = 600 cm with an Acrylic plate thickness of 3 mm (9 mm), respectively. The discrepancy between fitted and MC‐calculated SPRs at dref as a function of R50 is <0.8%, and in many cases <0.4%. The difference between fitted and MC‐calculated SPRs as a function of depth and R50 is within 1% at depths <0.8R50 for beams with R50 ≥ 1.14 cm. The ICRU‐90 recommendations decrease SPRs by 0.3%–0.4% compared to the use of data recommended in ICRU‐37. Conclusion The formulas used by the major protocols are accurate enough for clinical beams used in TSET and the error caused using the formulas is <1% to estimate SPRs as a function of depth and R50 for depths <0.8R50 for beams used in TSET with R50 ≥ 1.14 cm. The impact of the ICRU‐90 recommendations shows a decrease of SPRs by a fraction of a percent for beams used in TSET.

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Section: Introductionsupporting

confidence: 54%

Stopping‐power ratios for electron beams used in total skin electron therapy

Ding

2021

Medical Physics

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“…The absorbed dose measured using NACP chamber differed by about 1.5% in TRS 398 and TG 51 versus that of DIN 6800-2, while the corresponding figure obtained using the FC65-G chamber deviated by about 1.6%. These values agree with the results previously reported in the literature [13][14][15]. Our results show a high degree of consistency with the measurement uncertainty between the IAEA TRS 398 and DIN 6800-2.…”

Section: Resultssupporting

confidence: 93%

“…The results of parallel plate chambers are expected to differ from those of cylindrical chambers due to differences in the perturbation correction factors included in the radiation quality correction factors [15]. Because of this, correction factors for beam quality vary depending on the type of ionization chamber used.…”

Section: Discussionmentioning

confidence: 99%

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties

Elbashir

Ksouri

Eisa

et al. 2021

Life

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This paper presents guidelines for the calibration of radiation beams that were issued by the International Atomic Energy Agency (IAEA TRS 398), the American Association of Physicists in Medicine (AAPM TG 51) and the German task group (DIN 6800-2). These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standard laboratory’s reference quality beam, where the previous protocols were based on air kerma standards. This study aims to determine uncertainties in dosimetry for electron beam radiotherapy using internationally established high-energy radiotherapy beam calibration standards. Methods: Dw was determined in 6-, 12- and 18 MeV electron energies under reference conditions using three cylindrical and two plane-parallel ion chambers in concert with the IAEA TRS 398, AAPM TG 51 and DIN 6800-2 absorbed dose protocols. From mean measured Dw values, the ratio TRS 398/TG 51 was found to vary between 0.988 and 1.004, while for the counterpart TRS 398/DIN 6800-2 and TG 51/DIN 6800-2, the variation ranges were 0.991–1.003 and 0.997–1.005, respectively. For the cylindrical chambers, the relative combined uncertainty (k = 1) in absorbed dose measurements was 1.44%, while for the plane-parallel chambers, it ranged from 1.53 to 1.88%. Conclusions: A high degree of consistency was demonstrated among the three protocols. It is suggested that in the use of the presently determined dose conversion factors across the three protocols, dose intercomparisons can be facilitated between radiotherapy centres.

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“…The research pertaining to M Q and N D,w is more detailed, and it is difficult to reduce uncertainties in the determination. In contrast, research into the k Q factor is mostly limited to Monte Carlo (MC) simulations [7][8][9][10][11][12][13][14], and a few laboratories have given the experimental values of k Q for certain detectors [15][16][17][18][19][20]. Ion chamber specifications are rapidly being updated; hence, determining the ion chamber k Q factor remains an important area in the application of absorbed-dose standards.…”

Section: Beam Quality Conversion Factormentioning

confidence: 99%

Development and application of absorbed dose primary standard for ⁶⁰Co and high-energy photon beams using water calorimetry

Wang

Jin

et al. 2023

Metrologia

Self Cite

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Several new glass vessels, thermistor probes, and water phantoms have been designed and built at the National Institute of Metrology (China) to upgrade and develop the existing water calorimeter. The increased plane-parallel vessels have shorter thermal stability times and shallower positioning depths (~1.3 cm) than the previous cylindrical vessels, which makes them suitable for electron beams. The sensitivity of the new probes is 10% greater than the previous ones. In this study, detailed experimental and theoretical investigations of various factors affecting the new water calorimeter are performed. The system uncertainty of the water calorimeter is reduced and the robustness of the determination of the absorbed-dose-to-water D w is improved using a variety of geometric detector vessels and two kinds of high-purity water systems saturated with high-purity gases. This new calorimeter is employed as a primary standard for determining the D w, has achieved a combined standard uncertainty of 0.24% for a 60Co beam, 0.27% for 6 MV and 10MV photon beams and 0.30% for a 25 MV photon beam. The beam quality conversion factors kQ of ten cylindrical and three plane-parallel ionization chambers are measured using the new calorimeter to improve the reference dosimetry accuracy of high-energy clinical photon beams.

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Direct measurement of ionization chamber absorbed dose k factors in clinical electron beams

Cited by 6 publications

References 21 publications

Stopping‐power ratios for electron beams used in total skin electron therapy

Stopping‐power ratios for electron beams used in total skin electron therapy

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties

Development and application of absorbed dose primary standard for ⁶⁰Co and high-energy photon beams using water calorimetry

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Direct measurement of ionization chamber absorbed dose k factors in clinical electron beams

Cited by 6 publications

References 21 publications

Stopping‐power ratios for electron beams used in total skin electron therapy

Stopping‐power ratios for electron beams used in total skin electron therapy

Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties

Development and application of absorbed dose primary standard for 60Co and high-energy photon beams using water calorimetry

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Development and application of absorbed dose primary standard for ⁶⁰Co and high-energy photon beams using water calorimetry