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Use of Cylindrical Chambers as Substitutes for Parallel-Plate Chambers in Low-Energy Electron Dosimetry
Prog. Med. Phys. 2018;29(1):16-22
Published online March 31, 2018
© 2018 Korean Society of Medical Physics.

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, Department of Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Biomedical Research Institute, Seoul National University Hospital, §Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul, ΙΙCenter for Convergence Research on Robotics, Advanced Institutes of Convergence Technology, Suwon, Korea
Correspondence to: Jung-in Kim(madangin@gmail.com)
Tel: 82-2-2072-3573
Fax: 82-2-765-3317
Received February 28, 2018; Revised March 28, 2018; Accepted March 29, 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/4.0) 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


June 2018, 29 (2)