Fasala Ashleigh, Carr Madeline, Surjan Yolanda, Daghigh Parmoun, de Leon Jeremy, Burns Abbey, Batumalai Vikneswary
GenesisCare, Sydney, New South Wales, Australia.
College of Health, Medicine and Wellbeing, School of Health Sciences, Global Centre for Research and Training in Radiation Oncology, The University of Newcastle, Callaghan, New South Wales, Australia.
J Med Radiat Sci. 2025 Mar;72(1):17-24. doi: 10.1002/jmrs.832. Epub 2024 Oct 13.
Online adaptive radiotherapy is well suited for stereotactic ablative radiotherapy (SABR) in pancreatic cancer due to considerable intrafractional tumour motion. This study aimed to assess intrafraction motion and generate adjusted planning target volume (PTV) margins required for online adaptive radiotherapy in pancreatic cancer treatment using abdominal compression on the magnetic resonance linear accelerator (MR-Linac).
Motion monitoring images obtained from 67 fractions for 15 previously treated pancreatic cancer patients were analysed. All patients received SABR (50 Gy in five fractions) on the MR-Linac using abdominal compression. The analysis included quantification of intrafraction motion, leading to the development of adjusted PTV margins. The dosimetric impact of implementing the adjusted PTV was then evaluated in a cohort of 20 patients.
Intrafraction motion indicated an average target displacement of 1-3 mm, resulting in an adjusted PTV margin of 2 mm in the right-left and superior-inferior directions, and 3 mm in the anterior-posterior direction. Plans incorporating these adjusted margins consistently demonstrated improved dose to target volumes, with improvements averaging 1.5 Gy in CTV D99%, 4.9 Gy in PTV D99% and 1.2 Gy in PTV-high D90%, and better sparing of the organs at risk (OAR).
The improved target volume coverage and reduced OAR dose suggest potential for reducing current clinical margins for MR-Linac treatment. However, it is important to note that decreasing margins may reduce safeguards against geographical misses. Nonetheless, the continued integration of gating systems on MR-Linacs could provide confidence in adopting reduced margins.
由于胰腺癌在分次治疗期间存在显著的肿瘤运动，在线自适应放疗非常适合胰腺癌的立体定向消融放疗（SABR）。本研究旨在评估分次治疗期间的运动情况，并生成在磁共振直线加速器（MR-Linac）上使用腹部压迫进行胰腺癌在线自适应放疗所需的调整后计划靶区（PTV）边界。
分析了15例既往接受治疗的胰腺癌患者67个分次的运动监测图像。所有患者在MR-Linac上使用腹部压迫接受SABR（5次分次，共50 Gy）。分析包括分次治疗期间运动的量化，从而制定调整后的PTV边界。然后在20例患者队列中评估实施调整后PTV的剂量学影响。
分次治疗期间的运动显示平均靶位移为1 - 3毫米，导致在左右和上下方向调整后的PTV边界为2毫米，前后方向为3毫米。纳入这些调整后边界的计划始终显示靶区剂量有所改善，CTV D99%平均提高1.5 Gy，PTV D99%平均提高4.9 Gy，PTV-high D90%平均提高1.2 Gy，并且对危及器官（OAR）的保护更好。
靶区覆盖的改善和OAR剂量的降低表明有可能减少当前MR-Linac治疗的临床边界。然而，需要注意的是，减小边界可能会降低防止几何遗漏的保障措施。尽管如此，MR-Linac上继续集成门控系统可以为采用减小的边界提供信心。
