1. Stoichiometric CT number calibration using three-parameter fit model for ion therapy
- Author
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Minoru, Nakao, Masahiro, Hayata, Shuichi, Ozawa, Hideharu, Miura, Kiyoshi, Yamada, Daisuke, Kawahara, Kentaro, Miki, Takeo, Nakashima, Yusuke, Ochi, Shintaro, Tsuda, Mineaki, Seido, Yoshiharu, Morimoto, Atsushi, Kawakubo, Hiroshige, Nozaki, Kosaku, Habara, and Yasushi, Nagata
- Subjects
Phantoms, Imaging ,Radiotherapy Planning, Computer-Assisted ,Calibration ,Biophysics ,Water ,General Physics and Astronomy ,Radiology, Nuclear Medicine and imaging ,General Medicine ,Tomography, X-Ray Computed - Abstract
Treatment planning for ion therapy involves the conversion of computed tomography number (CTN) into a stopping-power ratio (SPR) relative to water. The purpose of this study was to create a CTN-to-SPR calibration table using a stoichiometric CTN calibration model with a three-parameter fit model for ion therapy, and to demonstrate its effectiveness by comparing it with a conventional stoichiometric CTN calibration model.We inserted eight tissue-equivalent materials into a CTN calibration phantom and used six CT scanners at five radiotherapy institutes to scan the phantom. We compared the theoretical CTN-to-SPR calibration tables created using the three-parameter fit and conventional models to the measured CTN-to-SPR calibration table in three tissue types: lung, adipose/muscle, and cartilage/spongy bone. We validated the estimated SPR differences in all cases and in a worst-case scenario, which revealed the largest estimated SPR difference in lung tissue.For all cases, the means ± standard deviations of the estimated SPR difference for the three-parameter fit method model were -0.1 ± 1.0%, 0.3 ± 0.7%, and 2.4 ± 0.6% for the lung, adipose/muscle, and cartilage/spongy bone, respectively. For the worst-case scenario, the estimated SPR differences of the conventional and the three-parameter fit models were 2.9% and -1.4% for the lung tissue, respectively.The CTN-to-SPR calibration table of the three-parameter fit model was consistent with that of the measurement and decreased the calibration error for low-density tissues, even for the worst-case scenario.
- Published
- 2022