Tetsurou Katayose1,2, Hidetoshi Saitoh3, Mitsunobu Igari4, Weishan Chang3, Shimpei Hashimoto5, Mie Morioka5. 1. Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo, Japan. tkatayose@gmail.com. 2. Chiba Cancer Center, 666-2 Nitona-chou, Chuo-ku, Chiba, Japan. tkatayose@gmail.com. 3. Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Higashiogu, Arakawa-ku, Tokyo, Japan. 4. Saitama Medical University International Medical Center, 1397-1 Yamane, Hidaka-shi, Saitama, Japan. 5. Tokyo Metropolitan Cancer and Infectious Diseases Center Komagome Hospital, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo, Japan.
Abstract
PURPOSE: The JSMP01 dosimetry protocol had adopted the provisional 60Co calibration coefficient [Formula: see text], namely, the product of exposure calibration coefficient N C and conversion coefficient k D,X. After that, the absorbed dose to water D w standard was established, and the JSMP12 protocol adopted the [Formula: see text] calibration. In this study, the influence of the calibration shift on the measurement of D w among users was analyzed. MATERIALS AND METHODS: The intercomparison of the D w using an ionization chamber was annually performed by visiting related hospitals. Intercomparison results before and after the calibration shift were analyzed, the deviation of D w among users was re-evaluated, and the cause of deviation was estimated. RESULTS: As a result, the stability of LINAC, calibration of the thermometer and barometer, and collection method of ion recombination were confirmed. The statistical significance of standard deviation of D w was not observed, but that of difference of D w among users was observed between N C and [Formula: see text] calibration. CONCLUSION: Uncertainty due to chamber-to-chamber variation was reduced by the calibration shift, consequently reducing the uncertainty among users regarding D w. The result also pointed out uncertainty might be reduced by accurate and detailed instructions on the setup of an ionization chamber.
PURPOSE: The JSMP01 dosimetry protocol had adopted the provisional 60Co calibration coefficient [Formula: see text], namely, the product of exposure calibration coefficient N C and conversion coefficient k D,X. After that, the absorbed dose to water D w standard was established, and the JSMP12 protocol adopted the [Formula: see text] calibration. In this study, the influence of the calibration shift on the measurement of D w among users was analyzed. MATERIALS AND METHODS: The intercomparison of the D w using an ionization chamber was annually performed by visiting related hospitals. Intercomparison results before and after the calibration shift were analyzed, the deviation of D w among users was re-evaluated, and the cause of deviation was estimated. RESULTS: As a result, the stability of LINAC, calibration of the thermometer and barometer, and collection method of ion recombination were confirmed. The statistical significance of standard deviation of D w was not observed, but that of difference of D w among users was observed between N C and [Formula: see text] calibration. CONCLUSION: Uncertainty due to chamber-to-chamber variation was reduced by the calibration shift, consequently reducing the uncertainty among users regarding D w. The result also pointed out uncertainty might be reduced by accurate and detailed instructions on the setup of an ionization chamber.
Entities:
Keywords:
Absorbed dose to water; Ionization chamber; Radiotherapy; Standard dosimetry; Uncertainty
Authors: Indra J Das; Chee-Wai Cheng; Ronald J Watts; Anders Ahnesjö; John Gibbons; X Allen Li; Jessica Lowenstein; Raj K Mitra; William E Simon; Timothy C Zhu Journal: Med Phys Date: 2008-09 Impact factor: 4.071