Use of Cylindrical Chambers as Substitutes for Parallel-Plate Chambers in Low-Energy Electron Dosimetry

Minsoo Chun; Hyun Joon An; Seong-Hee Kang; Jin Dong Cho; Jong Min Park; Jung-in Kim

doi:10.14316/pmp.2018.29.1.16

Journal List > Prog Med Phys > v.29(1) > 1098597

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Chun, An, Kang, Cho, Park, and Kim: Use of Cylindrical Chambers as Substitutes for Parallel-Plate Chambers in Low-Energy Electron Dosimetry

Original Article

Progress in Medical Physics 2018;29(1):16-22.

Published online: 20 March 2018

DOI: https://doi.org/10.14316/pmp.2018.29.1.16

Use of Cylindrical Chambers as Substitutes for Parallel-Plate Chambers in Low-Energy Electron Dosimetry

Minsoo Chun^∗, Hyun Joon An^∗, Seong-Hee Kang^†, Jin Dong Cho^‡, Jong Min Park^∗,^†,^‡,^§,^ΙΙ, Jung-in Kim^∗,^‡,^§

^∗Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea

^†Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea

^‡Biomedical Research Institute, Seoul National University Hospital, Seoul, Korea

^§Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, Korea

^ΙΙCenter for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Korea

Corresponding author Jung-in Kim (madangin@gmail.com) Tel: 82-2-2072-3573 Fax: 82-2-765-3317

Received 28 February 2018 Revised 28 March 2018 Accepted 29 March 2018

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Current dosimetry protocols recommend the use of parallel-plate chambers in electron dosimetry because the electron fluence perturbation can be effectively minimized. However, substitutable methods to calibrate and measure the electron output and energy with the widely used cylindrical chamber should be developed in case a parallel-plate chamber is unavailable. In this study, we measured the correction factors and absolute dose-to-water of electrons with energies of 4, 6, 9, 12, 16, and 20 MeV using Farmer-type and Roos chambers by varying the dose rates according to the AAPM TG-51 protocol. The ion recombination factor and absolute dose were found to be varied across the chamber types, energy, and dose rate, and these phenomena were remarkable at a low energy (4 MeV), which was in good agreement with literature. While the ion recombination factor showed a difference across chamber types of less than 0.4%, the absolute dose differences between them were largest at 4 MeV at approximately 1.5%. We therefore found that the absolute dose with respect to the dose rate was strongly influenced by ion-collection efficiency. Although more rigorous validation with other types of chambers and protocols should be performed, the outcome of the study shows the feasibility of replacing the parallel-plate chamber with the cylindrical chamber in electron dosimetry.

Keywords: Electron dosimetry, AAPM TG-51, Parallel plate chamber, Farmer chamber

References

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Fig. 1.

Used ion chambers (a) Farmer-type chamber, and (b) Roos chamber.

Fig. 2.

Differences in (a) ion recombination factors (P_ion), and (b) dose across two different chamber types.

Fig. 3.

The impact of dose rate on dosimetric parameters with an order of ion recombination factor (P_ion), collected charge, and the absolute dose. Measurements with (a) Farmer-type chamber, and (b) Roos chamber.

Table 1.

Numerical values for ion recombination factor (P_ion), and dose according to the chamber-type, energy, and dose rate.

Dose rate	Ion recombination factor (P_ion)						Dose (cGy)
Dose rate	4 MeV	6 MeV	9 MeV	12 MeV	16 MeV	20 MeV	4 MeV	6 MeV	9 MeV	12 MeV	16 MeV	20 MeV
Farmer chamber
100 MU/min	1.006	1.012	1.009	1.009	1.008	1.010	100.355	100.080	99.676	99.735	99.661	99.072
300 MU/min	1.008	1.012	1.010	1.010	1.008	1.011	100.748	100.156	99.776	99.910	99.635	99.277
600 MU/min	1.007	1.011	1.010	1.010	1.008	1.010	100.799	100.154	99.875	100.032	99.709	99.174
1,000 MU/min	1.009	1.011	1.011	1.010	1.010	1.011	101.219	100.302	100.176	100.104	100.078	99.325
Roos chamber
100 MU/min	1.008	1.011	1.009	1.010	1.008	1.010	101.852	99.620	100.012	100.459	100.039	98.962
300 MU/min	1.009	1.010	1.009	1.011	1.009	1.011	102.060	99.579	100.012	100.539	100.196	99.283
600 MU/min	1.011	1.012	1.011	1.011	1.012	1.013	102.434	100.064	100.450	100.697	100.703	99.565
1,000 MU/min	1.009	1.012	1.010	1.009	1.011	1.012	102.222	100.064	100.327	100.496	100.623	99.441

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