Department of Radiation Oncology, Mayo Clinic, 5881 East Mayo Blvd, Phoenix, AZ, 85054, USA.
Radiat Oncol. 2023 Sep 22;18(1):157. doi: 10.1186/s13014-023-02323-3.
Setup reproducibility of the tissue in the proton beam path is critical in maintaining the planned clinical target volume (CTV) dose coverage and sparing the organs at risk (OAR). In this study, we retrospectively evaluated radiation therapy dose reproducibility for proton pencil beam scanning (PBS) treatment of breast cancer patients with and without mask immobilization.
Ninety-four patients treated between January 2019 and September 2022 with at least one verification CT scan (V-CT) in treatment position were included for this study. All patients were set up with arms up using the Orfit AIO patient positioning system, with (69 patients) or without (25 patients) mask immobilization in chin, neck, shoulder, upper arm, and chest areas. Two to three enface or near enface single field uniform dose PBS beams were optimized using a commercial treatment planning system. Prescription doses were 25 to 60 Gy in 5 to 45 fractions. Treatment plan doses re-calculated on V-CTs were compared to the corresponding planned doses. Cumulative doses were also calculated for patients with at least 3 V-CTs by deform and weighted sum doses from V-CTs to corresponding P-CTs. CTV D95%, ipsilateral-lung V40%, esophagus D0.01cc, and heart mean dose were evaluated and reported as percentages of prescription doses. Differences were large dose deteriorations (LDD) if: (1) CTV (V-CT/cumulative D95%) - (Planned D95%) < - 5%; or (2) Ipsilateral-lung (V-CT/cumulative V40%) - (Planned V40%) > 5%; or (3) Esophagus (V-CT/cumulative D0.01cc) - (Planned D0.01cc) > 10%; or (4) Heart (V-CT/cumulative mean) - (Planned mean) > 1.5%.
On average, V-CT/cumulative and planned CTV/OAR dose parameter differences were less than 2.2%/1.7% and 3.4%/3.7% for masked and maskless patients, respectively. The percentages of patients with at least one CTV or OAR V-CT/cumulative dose LDD were 20.3%/25.0% and 72.0%/54.0% for masked and maskless patients, respectively.
On average, masked/maskless setups achieved delivered and planned CTV/OAR dose parameters agreed within 2.2%/3.7% for PBS treatment of breast cancer patients in this study. Maskless patients had higher rate of CTV/OAR LDDs compared to masked patients. Dosimetric differences large enough to raise clinical concerns in either group were able to be addressed with replannings.
在质子束路径中保持组织设置的可重复性对于维持计划的临床靶区（CTV）剂量覆盖和保护危及器官（OAR）至关重要。在这项研究中，我们回顾性评估了有和没有面罩固定的乳腺癌患者接受质子铅笔束扫描（PBS）治疗的放射治疗剂量可重复性。
本研究纳入了 2019 年 1 月至 2022 年 9 月期间至少有一次治疗位置验证 CT 扫描（V-CT）的 94 名患者。所有患者均采用 Orfit AIO 患者定位系统将手臂置于上方，其中 69 名患者采用面罩固定在颏、颈、肩、上臂和胸部区域，25 名患者不采用面罩固定。使用商业治疗计划系统优化了 2 到 3 个面或近面单场均匀剂量 PBS 束。处方剂量为 25 至 60 Gy，5 至 45 个分次。将 V-CT 上重新计算的治疗计划剂量与相应的计划剂量进行比较。对于至少有 3 个 V-CT 的患者，通过变形和从 V-CT 到相应 P-CT 的加权和剂量计算累积剂量。评估并报告 CTV D95%、同侧肺 V40%、食管 D0.01cc 和心脏平均剂量作为处方剂量的百分比。如果出现以下情况，则认为是大剂量恶化（LDD）：（1）CTV（V-CT/累积 D95%）-（计划 D95%） < -5%；或（2）同侧肺（V-CT/累积 V40%）-（计划 V40%） > 5%；或（3）食管（V-CT/累积 D0.01cc）-（计划 D0.01cc） > 10%；或（4）心脏（V-CT/累积平均）-（计划平均） > 1.5%。
平均而言，对于有面罩和无面罩的患者，V-CT/累积和计划 CTV/OAR 剂量参数差异分别小于 2.2%/1.7%和 3.4%/3.7%。至少有一个 CTV 或 OAR V-CT/累积剂量 LDD 的患者百分比分别为 20.3%/25.0%和 72.0%/54.0%，对于有面罩和无面罩的患者。
在这项研究中，对于接受 PBS 治疗的乳腺癌患者，平均而言，有面罩和无面罩的设置实现了递送和计划的 CTV/OAR 剂量参数之间的一致性，差异在 2.2%/3.7%以内。与有面罩的患者相比，无面罩的患者发生 CTV/OAR LDD 的比例更高。在这两组中，能够通过重新计划来解决足以引起临床关注的剂量差异。
