UNASSIGNED: Ten locally advanced pancreatic cancer patients were treated with 50 Gy in five fractions with intensity-modulated respiratory-gated radiation therapy on a 0.35-T MR-Linac. Patients received both pre- and post-treatment volumetric MRIs for each fraction. Gastrointestinal organs at risk (GI-OARs) were delineated on the pre-treatment MRI during the online ART process and retrospectively on the post-treatment MRI. The treated dose distribution for each adaptive plan was assessed on the post-treatment anatomy. Prescribed dose volume histogram metrics for the scheduled plan on the pre-treatment anatomy, the adapted plan on the pre-treatment anatomy, and the adapted plan on post-treatment anatomy were compared to the OAR-defined criteria for adaptation: the volume of the GI-OAR receiving greater than 33 Gy (V33Gy) should be ≤1 cubic centimeter.
UNASSIGNED: Across the 50 adapted plans for the 10 patients studied, 70% were adapted to meet the duodenum constraint, 74% for the stomach, 12% for the colon, and 48% for the small bowel. Owing to intrafraction organ motion, at the time of post-treatment imaging, the adaptive criteria were exceeded for the duodenum in 62% of fractions, the stomach in 36%, the colon in 10%, and the small bowel in 48%. Compared to the scheduled plan, the post-treatment plans showed a decrease in the V33Gy, demonstrating the benefit of plan adaptation for 66% of the fractions for the duodenum, 95% for the stomach, 100% for the colon, and 79% for the small bowel.
UNASSIGNED: Post-treatment images demonstrated that over the course of the adaptive plan generation and delivery, the GI-OARs moved from their isotoxic low-dose region and nearer to the dose-escalated high-dose region, exceeding dose-volume constraints. Intrafraction motion can have a significant dosimetric impact; therefore, measures to mitigate this motion are needed. Despite consistent intrafraction motion, plan adaptation still provides a dosimetric benefit.
■10例局部晚期胰腺癌患者在0.35-TMR-Linac上接受5个部分的50Gy调强呼吸门控放射治疗。对于每个部分,患者接受治疗前和治疗后的体积MRI。在在线ART过程中,在治疗前MRI上描绘了胃肠道危险器官(GI-OAR),并在治疗后MRI上进行了回顾性描述。在治疗后解剖结构上评估每个适应性计划的治疗剂量分布。针对治疗前解剖结构上的计划计划的规定剂量体积直方图度量,关于治疗前解剖结构的适应性计划,将治疗后解剖结构的适应计划与OAR定义的适应标准进行了比较:接受大于33Gy(V33Gy)的GI-OAR的体积应≤1立方厘米。
■在研究的10名患者的50个调整计划中,70%的人适应了十二指肠的限制,74%为胃,结肠12%,小肠占48%。由于内部器官运动,在治疗后成像时,十二指肠在62%的部分中超过了适应性标准,36%的胃,10%的结肠,小肠占48%。与预定计划相比,治疗后的计划显示V33Gy下降,证明计划适应十二指肠66%的部分的好处,95%的胃,100%的结肠,小肠占79%。
■后处理图像表明,在自适应计划的生成和交付过程中,GI-OAR从其等氧低剂量区域移动到更靠近剂量递增的高剂量区域,超过剂量体积限制。帧内运动会产生显著的剂量测定影响;因此,需要采取措施减轻这种运动。尽管一致的内部运动,计划适应仍然提供剂量测定的好处。