Fujita Health University, School of Health Sciences, Faculty of Radiological Technology, Toyoake, Aichi, Japan.
Anjo Kosei Hospital, Anjo, Aichi, Japan.
J Cancer Res Ther. 2023 Apr;19(Supplement):S0. doi: 10.4103/jcrt.jcrt_389_21.
The spot position is an important beam parameter in the quality assurance of scanning proton therapy. In this study, we investigated dosimetric impact of systematic 15 spot position errors (SSPE) in spot scanning proton therapy using three types of optimization methods of head and neck tumor.
The planning simulation was performed with ± 2 mm model SSPE in the X and Y directions. Treatment plans were created using intensity-modulated proton therapy (IMPT) and single-field uniform dose (SFUD). IMPT plans were created by two optimization methods: with worst-case optimization (WCO-IMPT) and without (IMPT). For clinical target volume (CTV), D95%, D50%, and D2cc were used for analysis. For organs at risk (OAR), Dmean was used to analyze the brain, cochlea, and parotid, and Dmax was used to analyze brainsetem, chiasm, optic nerve, and cord.
For CTV, the variation (1 standard deviation) of D95% was ± 0.88%, 0.97% and 0.97% to WCO-IMPT, IMPT, and SFUD plan. The variation of D50% and D2cc of CTV showed <0.5% variation in all plans. The dose variation due to SSPE was larger in OAR, and worst-case optimization reduced the dose variation, especially in Dmax. The analysis results showed that SSPE has little impact on SFUD.
We clarified the impact of SSPE on dose distribution for three optimization methods. SFUD was shown to be a robust treatment plan for OARs, and the WCO can be used to increase robustness to SSPE in IMPT.
在扫描质子治疗的质量保证中，斑点位置是一个重要的射束参数。本研究通过三种头颈部肿瘤的优化方法，探讨了斑点扫描质子治疗中 15 个斑点位置误差（SSPE）的剂量学影响。
在 X 和 Y 方向上对±2mm 的模型 SSPE 进行了规划模拟。采用强度调制质子治疗（IMPT）和单野均匀剂量（SFUD）方法创建治疗计划。IMPT 计划由两种优化方法创建：最坏情况优化（WCO-IMPT）和不进行优化（IMPT）。对于临床靶区（CTV），采用 D95%、D50%和 D2cc 进行分析。对于危及器官（OAR），采用 Dmean 分析脑、耳蜗和腮腺，采用 Dmax 分析脑脊髓、视交叉、视神经和脊髓。
对于 CTV，D95%的变化（1 个标准差）在 WCO-IMPT、IMPT 和 SFUD 计划中分别为±0.88%、0.97%和 0.97%。CTV 的 D50%和 D2cc 的变化在所有计划中均小于 0.5%。由于 SSPE，OAR 的剂量变化较大，而最坏情况优化降低了剂量变化，尤其是在 Dmax 方面。分析结果表明，SSPE 对 SFUD 的影响较小。
本研究阐明了三种优化方法中 SSPE 对剂量分布的影响。SFUD 对 OAR 是一种稳健的治疗计划，而 WCO 可用于增加 IMPT 对 SSPE 的稳健性。
