ESTRO 2025 - Abstract Book

S1445

Clinical - Lung

ESTRO 2025

[2] Sunassee ED,et al.PSI in an adaptive Bayesian approach to predict patient-specific RT responses.Int J of Rad Bio. 2019 [3] Prokopiou,et al.A PSI to predict radiation response and personalize RT fractionation.Rad Oncol,2015 [4] Walls GM,et al.Association between statin therapy dose intensity and radiation cardiotoxicity in NSCLC:Results from the NI-HEART study.Rad&Oncol. 2023 [5] Barrett S,et.al.Geometric and Dosimetric Evaluation of a Commercially Available Auto-segmentation Tool for Gross Tumour Volume Delineation in Locally Advanced Non-small Cell Lung Cancer: a Feasibility Study.Clin Oncol.2021

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Digital Poster Development and Clinical Implementation of an Adaptive Workflow for Biology-Guided Radiotherapy Using the PET-Linac Platform Bin Cai 1 , Girish Bal 2 , Chenyang Shen 1 , Rameshwar Prasad 1 , Thomas Banks 1 , Kenneth Westover 1 , Tu Dan 1 , Aurelie Garant 1 , David Sher 1 , Orhan Oz 3 , Robert Timmerman 1 , Shahed Badiyan 1 1 Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, USA. 2 RefleXion Medical, RefleXion Medical, Hayward, USA. 3 Radiology, University of Texas Southwestern Medical Center, Dallas, USA Purpose/Objective: SCINTIX therapy is a novel treatment strategy that utilizes real-time PET signals to guide radiotherapy delivery. This study aims to develop an adaptive workflow of SINCTIX treatment that integrates both anatomical and physiological changes for biology-guided radiotherapy using the PET-Linac platform. Material/Methods: The RefleXion X1 PET-Linac system, featuring two rotating PET detectors, kVCT, and a compact Linac, enables SCINTIX therapy. Initial SCINTIX plans are generated using simulation CT images, RT structure sets, and RefleXion functional modeling (FM) PET images. Before each treatment fraction, a localization kVCT and prescan PET are acquired to verify tumor FDG uptake and ensure treatment robustness. Evaluation metrics, including activity concentration (AC>5kBq/ml), normalized target signal (NTS>2) and gamma index (Gamma>95%) are reported. If prescan PET values fall outside the operating range, the initial plan is deemed unsuitable for delivery. To address this, our proposed adaptive workflow acquires a new FM PET scan immediately after the prescan using the same FDG injection during the same patient visit. An offline adaptation process is then initiated, involving updated RT structures on the localization kVCT (to account for anatomical changes) and the creation of an adaptive SCINTIX plan based on the updated FM PET (to account for biological changes) for subsequent treatment fractions. Results: The proposed workflow was successfully implemented in a clinical setting. In a five-fraction, 60 Gy lung SBRT case, prescan PET evaluation at fraction 3 failed due to a 77% reduction in tumor volume (from 11,826 mm³ to 2,679 mm³) and a 68% decrease in PET activity concentration (from 23.61 kBq/ml to 7.49 kBq/ml). An adaptive SCINTIX plan was created using updated target volumes on kVCT and FM PET, meeting the SCINTIX planning threshold with AC=14.3 kBq/ml and NTS=9.28. The adaptive plan reduced treatment time (39 minutes vs. 44 minutes) and lowered doses to the ribs (mean dose: 24 Gy vs. 29 Gy) and left lung (V20Gy=15% vs.17%) while maintaining comparable target coverage. These results demonstrate the feasibility and clinical benefits of the adaptive workflow in managing significant anatomical and physiological changes.