Chen Chin-Cheng, Liu Jiayi, Park Peter, Shim Andy, Huang Sheng, Wong Sarah, Tsai Pingfang, Lin Haibo, Choi J Isabelle
New York Proton Center, New York, NY, United States.
Institute of Nuclear Engineering and Science, National Tsing Hua University, Hsinchu, Taiwan.
Front Oncol. 2023 Jul 27;13:1132178. doi: 10.3389/fonc.2023.1132178. eCollection 2023.
Dose perturbation of spot-scanning proton beams passing through a dislocated metallic port (MP) of a breast tissue expander may degrade target dose coverage or deliver excess dose to the ipsilateral lung and heart. The feasibility of utilizing daily cone-beam computed tomography (CBCT)-based synthetic CTs (synCTs) for dose reconstruction was evaluated, and the fractional and cumulative dosimetric impact due to daily MP dislocation is reported.
The synCT was generated by deforming the simulation CT to daily CBCT. The MP structure template was mapped onto all CTs on the basis of daily MP position. Proton treatment plans were generated with two and three fields on the planned CT (pCT, Plan A) and the first verification CT (vCT, Plan B), respectively, for a fractional dose of 1.8 Gy(RBE). Plan A and Plan B were used alternatively, as determined by the daily MP position. The reconstructed fractional doses were calculated with corresponding plans and synCTs, and the cumulative doses were summed with the rigid or deformed fractional doses on pCT and vCT.
The planned and reconstructed fractional dose demonstrated a low-dose socket around the planned MP position due to the use of field-specific targets (FSTs). Dose hot spots with >120% of the prescription due to MP dislocation were found behind the planned MP position on most reconstructed fractional doses. The reconstructed cumulative dose shows two low-dose sockets around the two planned MP positions reflecting the two plans used. The doses at the hot spots behind the planned MPs averaged out to 114% of the prescription. The cumulative D of the CTV_Chest Wall decreased by up to 2.4% and 4.0%, and the cumulative V of the left lung decreased to 16.1% and 16.8% on pCT and vCT, respectively. The cumulative D of the heart decreased to as low as 0.7 Gy(RBE) on pCT but increased to as high as 1.6 Gy(RBE) on vCT.
The robustness of proton plans using FSTs around the magnet in the MP of the tissue expander can be improved by applying multiple fields and plans, which provides forgiveness of dose heterogeneity incurred from dislocation of high-Z materials in this single case.
通过乳腺组织扩张器的错位金属端口（MP）的点扫描质子束剂量扰动可能会降低靶区剂量覆盖或向同侧肺和心脏输送过量剂量。评估了利用基于每日锥束计算机断层扫描（CBCT）的合成CT（synCT）进行剂量重建的可行性，并报告了由于每日MP错位导致的分次和累积剂量学影响。
通过将模拟CT变形为每日CBCT生成synCT。基于每日MP位置将MP结构模板映射到所有CT上。分别在计划CT（pCT，计划A）和首次验证CT（vCT，计划B）上使用两个和三个射野生成质子治疗计划，分次剂量为1.8 Gy（RBE）。根据每日MP位置交替使用计划A和计划B。使用相应的计划和synCT计算重建的分次剂量，并将累积剂量与pCT和vCT上的刚性或变形分次剂量相加。
由于使用了射野特定靶区（FST），计划和重建的分次剂量在计划MP位置周围显示出低剂量凹陷。在大多数重建的分次剂量中，在计划MP位置后方发现由于MP错位导致的剂量热点超过处方剂量的120%。重建的累积剂量在两个计划MP位置周围显示出两个低剂量凹陷，反映了所使用的两个计划。计划MP后方热点处的剂量平均为处方剂量的114%。在pCT和vCT上，CTV_胸壁的累积D分别降低了2.4%和4.0%，左肺的累积V分别降至16.1%和16.8%。心脏的累积D在pCT上降至低至0.7 Gy（RBE），但在vCT上升至高达1.6 Gy（RBE）。
通过应用多个射野和计划，可以提高在组织扩张器MP中围绕磁体使用FST的质子计划的稳健性，这在这种单一情况下为高Z材料错位引起的剂量异质性提供了容错能力。
