Background/Objectives: This study aims to present a structured clinical workflow for offline adaptive Biology-guided Radiotherapy (BgRT) using the RefleXion X1 PET-linac system, addressing challenges introduced by inter-treatment anatomical and biological changes.Methods: We propose a decision tree offline adaptation framework based on real-time assessments of Activity Concentration (AC), Normalized Target Signal (NTS), and bounded dose-volume histogram (bDVH%) metrics. Three offline strategies were developed: (1) preemptive adaptation for minor changes, (2) partial re-simulation for moderate changes, and (3) full re-simulation for major anatomical or metabolic alterations. Two clinical cases demonstrating strategies 1 and 2 are presented.Results: The preemptive adaptation strategy was applied in a case with early tumor shrinkage, maintaining delivery parameters within acceptable limits while updating contours and dose distribution. In the partial re-Simulation case, significant changes in PET signal necessitated a same-day PET functional modeling session and plan re-optimization, effectively restoring safe deliverability. Both cases showed reduced target volumes and improved OAR sparing without additional patient visits or tracer injections.Conclusions: Offline adaptive workflows for BgRT provide practical solutions to address inter-fractional changes in tumor structure and function. These strategies can help maintain the safety and accuracy of BgRT delivery and support clinical adoption of PET-guided radiotherapy, paving the way for future online adaptive capabilities.
**背景/目的：** 本研究旨在提出一种基于RefleXion X1 PET-linac系统的离线自适应生物学引导放疗（BgRT）结构化临床工作流程，以应对分次治疗间解剖和生物学变化带来的挑战。 **方法：** 我们提出了一种基于实时评估活性浓度（AC）、归一化靶区信号（NTS）和有界剂量体积直方图（bDVH%）指标的决策树式离线自适应框架。开发了三种离线策略：（1）针对微小变化的预防性自适应；（2）针对中度变化的部分再模拟；（3）针对重大解剖或代谢改变的全部再模拟。文中展示了应用策略1和2的两个临床病例。 **结果：** 预防性自适应策略应用于一例早期肿瘤缩小的病例，在更新轮廓和剂量分布的同时，将照射参数维持在可接受范围内。在部分再模拟病例中，PET信号的显著变化需要在同一天进行PET功能建模和计划重新优化，从而有效恢复了治疗实施的安全性。两个病例均显示靶区体积减小，危及器官受照剂量降低，且无需患者额外就诊或注射示踪剂。 **结论：** BgRT的离线自适应工作流程为解决分次间肿瘤结构和功能变化提供了实用的解决方案。这些策略有助于维持BgRT治疗的安全性和准确性，支持PET引导放疗的临床应用，并为未来实现在线自适应能力铺平道路。
Strategies for Offline Adaptive Biology-Guided Radiotherapy (BgRT) on a PET-Linac Platform
肿瘤(癌症)患者之家