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Title: Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac

Abstract

Purpose: Microdosimetry has been developed for the evaluation of radiation quality, and single-event dose-mean lineal energy y{sub D} is well-used to represent the radiation quality. In this study, the changes of the relative biological effectiveness (RBE) values under the therapeutic conditions using a 6 MV linac were investigated with a microdosimetric method. Methods: The y{sub D} values under the various irradiation conditions for x-rays from a 6 MV linac were measured with a tissue-equivalent proportional counter (TEPC) at an extremely low dose rate of a few tens of {mu}Gy/min by decreasing the gun grid voltage of the linac. According to the microdosimetric kinetic model (MK model), the RBE{sub MK} values for cell killing of the human salivary gland (HSG) tumor cells can be derived if the y{sub D} values are obtained from TEPC measurements. The Monte Carlo code GEANT4 was also used to calculate the photon energy distributions and to investigate the changes of the y{sub D} values under the various conditions. Results: The changes of the y{sub D} values were less than approximately 10% when the field size and the depth in a phantom varied. However, in the measurements perpendicular to a central beam axis, large changes were observedmore » between the y{sub D} values inside the field and those outside the field. The maximum increase of approximately 50% in the y{sub D} value outside the field was obtained compared with those inside the field. The GEANT4 calculations showed that there existed a large relative number of low energy photons outside of the field as compared with inside of the field. The percentages of the photon fluences below 200 keV outside the field were approximately 40% against approximately 8% inside the field. By using the MK model, the field size and the depth dependence of the RBE{sub MK} values were less than approximately 2% inside the field. However, the RBE{sub MK} values outside the field were 6.6% higher than those inside the field. Conclusions: The increase of the RBE{sub MK} values by 6.6% outside the field was observed. This increase is caused by the change of the photon energy distributions, especially the increase of the relative number of low energy photons outside the field.« less

Authors:
; ; ; ; ; ; ; ;  [1]
  1. Department of Energy Sciences, Tokyo Institute of Technology, Kanagawa 226-8502, Japan and Radiation Oncology Division, National Cancer Center Hospital, Tokyo 104-0045 (Japan)
Publication Date:
OSTI Identifier:
22098598
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 38; Journal Issue: 8; Other Information: (c) 2011 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; 62 RADIOLOGY AND NUCLEAR MEDICINE; BEAMS; CELL KILLING; COMPUTERIZED SIMULATION; ENERGY SPECTRA; IRRADIATION; KEV RANGE; LINEAR ACCELERATORS; MICRODOSIMETRY; MONTE CARLO METHOD; PHOTONS; PROPORTIONAL COUNTERS; RADIATION DOSES; RADIATION QUALITY; SALIVARY GLANDS; TUMOR CELLS; X RADIATION

Citation Formats

Okamoto, Hiroyuki, Kohno, Toshiyuki, Kanai, Tatsuaki, Kase, Yuki, Matsumoto, Yoshitaka, Furusawa, Yoshiya, Fujita, Yukio, Saitoh, Hidetoshi, Itami, Jun, Department of Energy Sciences, Tokyo Institute of Technology, Kanagawa 226-8502, Heavy Ion Medical Center, Gunma University, Gunma 371-8511, Proton Therapy Division, Shizuoka Cancer Center Research Institute, Shizuoka 411-8777, Heavy-Ion Radiobiology Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo 116-8551, and Radiation Oncology Division, National Cancer Center Hospital, Tokyo 104-0045. Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac. United States: N. p., 2011. Web. doi:10.1118/1.3613152.
Okamoto, Hiroyuki, Kohno, Toshiyuki, Kanai, Tatsuaki, Kase, Yuki, Matsumoto, Yoshitaka, Furusawa, Yoshiya, Fujita, Yukio, Saitoh, Hidetoshi, Itami, Jun, Department of Energy Sciences, Tokyo Institute of Technology, Kanagawa 226-8502, Heavy Ion Medical Center, Gunma University, Gunma 371-8511, Proton Therapy Division, Shizuoka Cancer Center Research Institute, Shizuoka 411-8777, Heavy-Ion Radiobiology Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo 116-8551, & Radiation Oncology Division, National Cancer Center Hospital, Tokyo 104-0045. Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac. United States. https://doi.org/10.1118/1.3613152
Okamoto, Hiroyuki, Kohno, Toshiyuki, Kanai, Tatsuaki, Kase, Yuki, Matsumoto, Yoshitaka, Furusawa, Yoshiya, Fujita, Yukio, Saitoh, Hidetoshi, Itami, Jun, Department of Energy Sciences, Tokyo Institute of Technology, Kanagawa 226-8502, Heavy Ion Medical Center, Gunma University, Gunma 371-8511, Proton Therapy Division, Shizuoka Cancer Center Research Institute, Shizuoka 411-8777, Heavy-Ion Radiobiology Research Group, National Institute of Radiological Sciences, Chiba 263-8555, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo 116-8551, and Radiation Oncology Division, National Cancer Center Hospital, Tokyo 104-0045. 2011. "Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac". United States. https://doi.org/10.1118/1.3613152.
@article{osti_22098598,
title = {Microdosimetric study on influence of low energy photons on relative biological effectiveness under therapeutic conditions using 6 MV linac},
author = {Okamoto, Hiroyuki and Kohno, Toshiyuki and Kanai, Tatsuaki and Kase, Yuki and Matsumoto, Yoshitaka and Furusawa, Yoshiya and Fujita, Yukio and Saitoh, Hidetoshi and Itami, Jun and Department of Energy Sciences, Tokyo Institute of Technology, Kanagawa 226-8502 and Heavy Ion Medical Center, Gunma University, Gunma 371-8511 and Proton Therapy Division, Shizuoka Cancer Center Research Institute, Shizuoka 411-8777 and Heavy-Ion Radiobiology Research Group, National Institute of Radiological Sciences, Chiba 263-8555 and Graduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo 116-8551 and Radiation Oncology Division, National Cancer Center Hospital, Tokyo 104-0045},
abstractNote = {Purpose: Microdosimetry has been developed for the evaluation of radiation quality, and single-event dose-mean lineal energy y{sub D} is well-used to represent the radiation quality. In this study, the changes of the relative biological effectiveness (RBE) values under the therapeutic conditions using a 6 MV linac were investigated with a microdosimetric method. Methods: The y{sub D} values under the various irradiation conditions for x-rays from a 6 MV linac were measured with a tissue-equivalent proportional counter (TEPC) at an extremely low dose rate of a few tens of {mu}Gy/min by decreasing the gun grid voltage of the linac. According to the microdosimetric kinetic model (MK model), the RBE{sub MK} values for cell killing of the human salivary gland (HSG) tumor cells can be derived if the y{sub D} values are obtained from TEPC measurements. The Monte Carlo code GEANT4 was also used to calculate the photon energy distributions and to investigate the changes of the y{sub D} values under the various conditions. Results: The changes of the y{sub D} values were less than approximately 10% when the field size and the depth in a phantom varied. However, in the measurements perpendicular to a central beam axis, large changes were observed between the y{sub D} values inside the field and those outside the field. The maximum increase of approximately 50% in the y{sub D} value outside the field was obtained compared with those inside the field. The GEANT4 calculations showed that there existed a large relative number of low energy photons outside of the field as compared with inside of the field. The percentages of the photon fluences below 200 keV outside the field were approximately 40% against approximately 8% inside the field. By using the MK model, the field size and the depth dependence of the RBE{sub MK} values were less than approximately 2% inside the field. However, the RBE{sub MK} values outside the field were 6.6% higher than those inside the field. Conclusions: The increase of the RBE{sub MK} values by 6.6% outside the field was observed. This increase is caused by the change of the photon energy distributions, especially the increase of the relative number of low energy photons outside the field.},
doi = {10.1118/1.3613152},
url = {https://www.osti.gov/biblio/22098598}, journal = {Medical Physics},
issn = {0094-2405},
number = 8,
volume = 38,
place = {United States},
year = {Mon Aug 15 00:00:00 EDT 2011},
month = {Mon Aug 15 00:00:00 EDT 2011}
}