Background/Objectives:Non-ablative stereotactic body radiation therapy (SBRT) is commonly employed for locally advanced pancreatic cancer (LAPC) using computed tomography-guided radiotherapy (CTgRT) without online adaptive radiation therapy (oART). The safe delivery of ablative SBRT has been demonstrated using stereotactic magnetic resonance-guided online adaptive radiation therapy (SMART). We performed an in silico comparison of non-adapted CTgRT versus SMART to better understand the potential benefit of oART for ablative pancreatic SBRT.Methods:We retrospectively evaluated original and daily adapted SMART plans that were previously delivered for 20 consecutive LAPC cases (120 total plans across all patients) treated on a 0.35 T MR-linac prescribed to 50 Gy (gross disease) and 33 Gy (elective sites) simultaneously in five fractions. Six comparative CTgRT plans for each patient (one original, five daily treatment) were retrospectively generated with the same prescribed dose and planning parameters as the SMART plans assuming no oART availability. The impact of daily anatomic changes on CTgRT and SMART plans without oART was evaluated across each treatment day MRI scan acquired for SMART.Results:Ninety percent of cases involved the pancreatic head. No statistically significant differences were seen between CTgRT and SMART with respect to target coverage. Nearly all (96%) fractions planned on either CT or MRI platforms exceeded at least one GI organ at risk (OAR) constraint without oART. Significant differences favoring SMART over non-adaptive CTgRT were observed for the duodenum V35 Gy ≤ 0.5 cc (34.2 vs. 41.9 Gy,p= 0.0035) and duodenum V40 Gy ≤ 0.03 cc (37 vs. 52.5 Gy,p= 0.0006) constraints. Stomach V40 Gy trended towards significance favoring SMART (37 vs. 40.3 Gy,p= 0.057) while no significant differences were seen.Conclusions:This is the first study that quantifies the frequency and extent of GI OAR constraint violations that would occur during ablative five-fraction SBRT using SMART vs. CTgRT. GI OAR constraint violations are expected for most fractions without oART whereas all constraints can be achieved with oART. As such, these data suggest that oART should be required for ablative five-fraction pancreatic SBRT.
**背景/目的：** 对于局部晚期胰腺癌，通常采用非消融性立体定向体部放疗，并基于计算机断层扫描引导放疗技术，而不进行在线自适应放疗。已有研究证实，使用立体定向磁共振引导在线自适应放疗技术可安全实施消融性SBRT。本研究通过计算机模拟，比较了非自适应CTgRT与SMART方案，以深入理解oART在消融性胰腺SBRT中的潜在获益。 **方法：** 我们回顾性分析了连续20例LAPC患者（所有患者共计120个计划）先前在0.35 T MR-linac上实施的SMART计划（包括原始计划和每日自适应计划），处方剂量为50 Gy（大体肿瘤）和33 Gy（选择性靶区），分5次同步照射。为每位患者回顾性生成了6个对比性CTgRT计划（1个原始计划，5个每日治疗计划），其处方剂量和计划参数与SMART计划相同，但假设不具备oART功能。基于SMART治疗期间每日获取的MRI扫描，评估了每日解剖结构变化对非自适应CTgRT和SMART计划的影响。 **结果：** 90%的病例肿瘤位于胰头部。在靶区覆盖方面，CTgRT与SMART之间未观察到统计学显著差异。在无oART的情况下，几乎所有（96%）基于CT或MRI平台制定的分次计划，其至少一项胃肠道危及器官剂量限制被超出。在十二指肠V35 Gy ≤ 0.5 cc（34.2 vs. 41.9 Gy, p=0.0035）和十二指肠V40 Gy ≤ 0.03 cc（37 vs. 52.5 Gy, p=0.0006）的限制上，观察到SMART显著优于非自适应CTgRT。胃V40 Gy有倾向于SMART更优的趋势（37 vs. 40.3 Gy, p=0.057），但未达到显著差异。 **结论：** 这是首项量化比较使用SMART与CTgRT进行5次消融性SBRT时，胃肠道OAR剂量限制被违反的频率和程度的研究。在无oART的情况下，大多数分次治疗预计会出现胃肠道OAR剂量限制违反，而使用oART则可满足所有限制条件。因此，这些数据表明，对于5次消融性胰腺SBRT，oART是必要的。
肿瘤(癌症)患者之家