Department of Carbon Ion Radiotherapy, Osaka University Graduate School of Medicine, Suita-shi, Osaka, Japan.
Department of Medical Physics, Osaka Heavy Ion Therapy Center, Osaka-shi, Osaka, Japan.
PLoS One. 2023 Jul 28;18(7):e0288545. doi: 10.1371/journal.pone.0288545. eCollection 2023.
Currently, treatment planning systems (TPSs) that can compute the intensities of intensity-modulated carbon-ion therapy (IMCT) using scanned carbon-ion beams are limited. In the present study, the computational efficacy of the newly designed IMCT algorithms was analyzed for the first time based on the mixed beam model with respect to the physical and biological doses; moreover, the validity and effectiveness of the robust radiobiological optimization were verified. A dose calculation engine was independently generated to validate a clinical dose determined in the TPS. A biological assay was performed using the HSGc-C5 cell line to validate the calculated surviving fraction (SF). Both spot control (SC) and voxel-wise worst-case scenario (WC) algorithms were employed for robust radiobiological optimization followed by their application in a Radiation Therapy Oncology Group benchmark phantom under homogeneous and heterogeneous conditions and a clinical case for range and position errors. Importantly, for the first time, both SC and WC algorithms were implemented in the integrated TPS platform that can compute the intensities of IMCT using scanned carbon-ion beams for robust radiobiological optimization. For assessing the robustness, the difference between the maximum and minimum values of a dose-volume histogram index in the examined error scenarios was considered as a robustness index. The relative biological effectiveness (RBE) determined by the independent dose calculation engine exhibited a -0.6% difference compared with the RBE defined by the TPS at the isocenter, whereas the measured and the calculated SF were similar. Regardless of the objects, compared with the conventional IMCT, the robust radiobiological optimization enhanced the sensitivity of the examined error scenarios by up to 19% for the robustness index. The computational efficacy of the novel IMCT algorithms was verified according to the mixed beam model with respect to the physical and biological doses. The robust radiobiological optimizations lowered the impact of range and position uncertainties considerably in the examined scenarios. The robustness of the WC algorithm was more enhanced compared with that of the SC algorithm. Nevertheless, the SC algorithm can be used as an alternative to the WC IMCT algorithm with respect to the computational cost.
目前，能够使用扫描碳离子束计算强度调制碳离子治疗（IMCT）强度的治疗计划系统（TPS）有限。在本研究中，首次基于混合束模型分析了新设计的 IMCT 算法在物理和生物剂量方面的计算功效，同时验证了稳健放射生物学优化的有效性和实用性。为了验证 TPS 中确定的临床剂量，独立生成了一个剂量计算引擎。使用 HSGc-C5 细胞系进行了生物测定，以验证计算的存活分数（SF）。对于稳健放射生物学优化，使用点控制（SC）和体素最差情况（WC）算法，然后将其应用于均匀和非均匀条件下的放射治疗肿瘤学组基准体模以及范围和位置误差的临床病例中。重要的是，首次在可以使用扫描碳离子束计算 IMCT 强度的集成 TPS 平台中实现了 SC 和 WC 算法，用于稳健放射生物学优化。为了评估稳健性，将检查的误差情况下剂量-体积直方图指数的最大值和最小值之间的差异作为稳健性指数。由独立剂量计算引擎确定的相对生物效应（RBE）与在等中心处由 TPS 定义的 RBE 相比，差异为-0.6%，而测量和计算的 SF 相似。无论对象如何，与传统的 IMCT 相比，稳健放射生物学优化将检查的误差情况下的稳健性指数的敏感性提高了多达 19%。根据物理和生物剂量，通过混合束模型验证了新型 IMCT 算法的计算功效。稳健放射生物学优化在检查的场景中大大降低了范围和位置不确定性的影响。与 SC 算法相比，WC 算法的稳健性得到了更多的增强。然而，就计算成本而言，SC 算法可以作为 WC IMCT 算法的替代方案。
