Savla Bansi, Jatczak Jenna, Molitoris Jason K, Witek Matthew E, Marter Kimberly, Zakhary Mark J, Xu Junliang, Snow Grace E, Guardiani Elizabeth A, Ferris Matthew J
Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
Department of Radiation Medicine, MedStar Georgetown University Hospital, Washington, District of Columbia, USA.
Int J Part Ther. 2024 Jul 17;13:100623. doi: 10.1016/j.ijpt.2024.100623. eCollection 2024 Sep.
Single vocal cord irradiation (SVCI) is a promising technique to maintain excellent oncologic control and potentially improve upon toxicities for treatment of early-stage glottic squamous cell carcinomas. We sought to investigate whether pencil beam scanning (PBS) proton therapy could improve upon the already favorable dose gradients demonstrated with volumetric modulated arc therapy (VMAT) SVCI.
A 64-year-old gentleman was treated in our department with 6X-flattening filter-free VMAT SVCI to 58.08 Gy in 16 fractions for a T1a well-differentiated squamous cell carcinoma of the left true vocal cord and tolerated it well with good local control. Comparative PBS plans were created in Raystation for the Varian ProBeam with clinical target volume (CTVs) generated to mimic the prescription target volume extent of the VMAT planning target volumes when accounting for PBS plan robustness (±3 mm translational shifts, 3.5% density perturbation). A 3-field single-field optimization plan was selected as dosimetrically preferable. Dosimetric variables were compared.
Several organs at risk doses improved with PBS, including the maximum and mean dose to ipsilateral carotids, maximum and mean dose to contralateral carotid, maximum dose to the spinal cord, maximum and mean dose to inferior constrictor/cricopharyngeus, maximum and mean dose to the uninvolved vocal cord, and mean dose to the thyroid gland. There are tradeoffs in skin dose depending on location relative to the target-with the highest and lowest isodoses extending more into the skin with the VMAT plan but with the moderate isodose lines covering a wider area with the PBS plan, but we deemed it tolerable regardless.
SVCI is a promising strategy for maintaining the oncologic effectiveness of whole-larynx photon radiation while potentially improving upon the historic toxicity profile. The favorable dose distribution with PBS with respect to organs at risk dosimetry for PBS may allow for further improvements upon VMAT SVCI strategies. Clinical implementation of PBS SVCI may be considered.
单声带照射（SVCI）是一种有前景的技术，可在治疗早期声门鳞状细胞癌时保持良好的肿瘤控制效果，并可能改善毒性反应。我们试图研究笔形束扫描（PBS）质子治疗是否能在容积调强弧形放疗（VMAT）SVCI已显示出的良好剂量梯度基础上进一步改善。
一名64岁男性患者在我科接受了6X无均整器VMAT SVCI治疗，针对左侧真声带T1a高分化鳞状细胞癌给予16次分割、总剂量58.08 Gy的照射，患者耐受良好，局部控制效果良好。在Raystation中为Varian ProBeam创建了对比PBS计划，生成临床靶区（CTVs）以模拟VMAT计划靶区的处方靶区范围，并考虑PBS计划的稳健性（±3 mm平移移位，3.5%密度扰动）。选择了一个3野单野优化计划，因其剂量学表现更优。比较了剂量学变量。
PBS使多个危及器官的剂量得到改善，包括同侧颈动脉的最大剂量和平均剂量、对侧颈动脉的最大剂量和平均剂量、脊髓的最大剂量、下咽缩肌/环咽肌的最大剂量和平均剂量、未受累声带的最大剂量和平均剂量以及甲状腺的平均剂量。皮肤剂量存在权衡，这取决于相对于靶区的位置——VMAT计划中最高和最低等剂量线更多地延伸至皮肤，但PBS计划中等剂量线覆盖的面积更广，但我们认为无论哪种情况都是可耐受的。
SVCI是一种有前景的策略，可在维持全喉光子放疗肿瘤学有效性的同时，潜在地改善既往的毒性特征。PBS在危及器官剂量学方面的良好剂量分布可能使VMAT SVCI策略得到进一步改进。可考虑PBS SVCI的临床应用。
