Author: Min Cheol Han, Soorim Han, Chan Hyeong Kim, Jin Sung Kim, Seok-Ho Lee, Gahee Son, Yongdo Yun 👨🔬
Affiliation: Department of Radiation Oncology, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine, Hanyang University, Department of Integrative Medicine, Yonsei Cancer Center, Heavy Ion Therapy Research Institute, Yonsei University College of Medicine 🌍
Purpose: The stoichiometric calibration method proposed by Kanematsu et al. (2016) has been widely adopted for CT number to stopping-power ratio (SPR) conversion in carbon-ion radiotherapy. With the release of updated tissue composition data in International Commission on Radiological Protection (ICRP) Publication 145, this study aimed to evaluate the feasibility of revising the 11 representative tissues in the Kanematsu method using these new data. The CT-to-SPR curves generated using ICRP Publication 145 were compared with those from ICRP Publication 110 by calculating carbon-ion beam ranges to validate range prediction accuracy.
Methods: Tissue compositions and elemental weight fractions used to generate CT-to-SPR curves were extracted from ICRP Publications 110 and 145, respectively. Other parameters required for SPR generation—including relative electron density, mean excitation energy, and effective energy—were either kept constant or calculated according to the Kanematsu method. To validate the range accuracy of the generated CT-to-SPR curves, carbon-ion beam ranges were experimentally measured in lard, olive oil, milk, and potassium phosphate (K₂HPO₄) solutions, and compared with ranges calculated by the CT-to-SPR curves derived from both ICRP datasets.
Results: For tissue-equivalent materials (i.e., lard, olive oil, and milk), the updated method based on ICRP Publication 145 showed deviations of up to 0.3% from measured ranges, an improvement over the 1.1% discrepancy observed with ICRP Publication 110. For high-density K₂HPO₄ solutions, the updated method reduced range differences from 7.3% to 4.1%.
Conclusion: The revised CT-to-SPR calibration using ICRP Publication 145 data demonstrated improved range prediction accuracy compared to results derived from ICRP Publication 110. Future work will include Monte Carlo simulations for further validation. This update is expected to reduce range uncertainties in robust treatment planning for carbon-ion radiotherapy, potentially reducing clinical margins.