Author: Min Cheol Han, 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: This study aims to develop the MC-DOLCE, a Monte Carlo (MC)-based system capable of calculating physical and biological dose distributions, as well as linear energy transfer (LET) distributions, for carbon-ion radiotherapy (CIRT).
Methods: This MC-DOLCE, developed using TOPAS, calculates dose and LET distributions based on DICOM datasets (CT, RT-Structure and RT-Plan). The modified microdosimetric kinetic model was implemented into our system for biological dose calculations. Dose-averaged LET was derived by accounting for CIRT process, including primary ions and secondary fragments. Validation was performed using a plan irradiating a virtual target (3×3×6 cm³) in a water phantom. MC-calculated dose and LET distributions were compared with those calculated by a treatment planning system (TPS). After validation, the MC-DOLCE was applied to a prostate cancer patient case to compare MC-calculated dose and LET distributions with TPS results. All evaluations were conducted using gamma analysis (2 mm/2%) for dose comparisons and LET volume histograms (LETVH) for LET comparisons.
Results: In the water phantom, MC-calculated dose distributions showed excellent agreement with TPS results, achieving gamma pass rates of >99.9%. LET calculations in the target also showed consistency, with target LETmean values matching within 2.7%. In the patient case, dose distributions calculated by MC-DOLCE were compared with those from the TPS, resulting in gamma passing rates of >97.0%. The relative error in target LETmean between TPS and MC-DOLCE was 0.4%. For the bladder and rectum, the LETmean differences were 13.5% and 28.0%, respectively.
Conclusion: The purpose of this study is to develop a MC-based system to calculate dose and LET distributions for CIRT, validating excellent agreement with TPS for dose and LET distributions in homogeneous regions. However, differences in LET calculations for organs-at-risk were observed in inhomogeneous regions. We will apply the MC-DOLCE to complex clinical scenarios, such as lung and head-and-neck cases.