Stopping-Power Ratios for Dosimetry

Andreo, Pedro

doi:10.1007/978-1-4613-1059-4_23

Cited by 15 publications

(24 citation statements)

References 16 publications

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“…In the AAPM [26] notation, the p dis and p cav correction factors correspond to the gradient, P gr , and the fluence, P fl , correction factors, respectively. For the beam quality, TPR20,10 = 0.669, s w,air = 1.121323 [27], p dis × p cav = 0.998 [28], p wall = 0.991, and p cel = 1.000 [29]. Using these figures, the D w,point /D chamber ratio is 1.109, in agreement with the MC-calculated ratio of 1.112 (table 2).…”

Section: Discussionsupporting

confidence: 85%

Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams

Andersson

Swanpalmer

Palm

et al. 2023

Biomed. Phys. Eng. Express

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Purpose: To investigate the response of the CC13 ionization chamber under non-reference photon beam conditions, focusing on penumbra and build-up regions of static fields and on dynamic intensity-modulated beams. Methods: Measurements were performed in 6 MV 100 × 100, 20 × 100, and 20 × 20 mm2 static fields. Monte Carlo calculations were performed for the static fields and for 6 and 15 MV dynamic beam sequences using a Varian multi-leaf collimator. The chamber was modelled using EGSnrc egs_chamber software. Conversion factors were calculated by relating the absorbed dose to air in the chamber air cavity to the absorbed dose to water. Correction and point-dose correction factors were calculated to quantify the conversion factor variations. Results: The correction factors for positions on the beam central axis and at the penumbra centre were 0.98–1.02 for all static fields and depths investigated. The largest corrections were obtained for chamber positions beyond penumbra centre in the off-axis direction. Point-dose correction factors were 0.54–0.71 at 100 mm depth and their magnitude increased with decreasing field size and measurement depth. Factors of 0.99–1.03 were obtained inside and near the integrated penumbra of the dynamic field at 100 mm depth, and of 0.92–0.94 beyond the integrated penumbra centre. The variations in the ionization chamber response across the integrated dynamic penumbra qualitatively followed the behaviour across penumbra of static fields. Conclusions: Without corrections, the CC13 chamber was of limited usefulness for profile measurements in 20-mm-wide fields. However, measurements in dynamic small irregular beam openings resembling the conditions of pre-treatment patient quality assurance were feasible. Uncorrected ionization chamber response could be applied for dose verification at 100 mm depth inside and close to large gradients of dynamically accumulating high- and low-dose regions assuming 3% tolerance between measured and calculated doses.

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Section: Discussionsupporting

confidence: 85%

Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams

Andersson

Swanpalmer

Palm

et al. 2023

Biomed. Phys. Eng. Express

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“…Larger discrepancies were noted at some other depths. The dependence of water-to-air stoppingpower ratios on beam characteristics, energy spectra and photon contamination has thus been demonstrated by this and other studies in the literature (Nahum 1978, ICRU 1984a, Andreo 1988, Andreo and Fransson 1989, Klevenhagen 1994.…”

Section: Introductionsupporting

confidence: 74%

Energy-and Intensity-Modulated Electron Beam for Breast Cancer Treatment

Boyer¹

2003

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“…For AAPM TG-51 the water to air stopping power ratios were calculated with the equation given by Rogers and Yang (1999) whereas P repl and P wall were calculated according to Rogers (1996). For IAEA TRS-398 the water to air stopping power ratios were calculated with the third-degree polynomial given by Andreo (1994), p wall with the expression and data recommended in IAEA TRS-398 and p dis with the data of Johansson et al (1977). The stopping power data points for the beams of this study deviate slightly (not more than 0.15%) from the data for the theoretical TPR 20,10 -%dd(10) x relationship.…”

Section: Discussion Of Datamentioning

confidence: 99%

Absorbed dose to water based dosimetry versus air kerma based dosimetry for high-energy photon beams: an experimental study

et al. 2002

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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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Stopping-Power Ratios for Dosimetry

Cited by 15 publications

References 16 publications

Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams

Cylindrical ionization chamber response in static and dynamic 6 and 15 MV photon beams

Energy-and Intensity-Modulated Electron Beam for Breast Cancer Treatment

Absorbed dose to water based dosimetry versus air kerma based dosimetry for high-energy photon beams: an experimental study

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