Author: Shahed Badiyan, Girish Bal, Thomas I. Banks, Bin Cai, Tu Dan, Aurelie Garant, Andrew R. Godley, Steve Jiang, Orhan Oz, Arnold Pompos, Rameshwar Prasad, Chenyang Shen, David Sher, Robert Timmerman, Kenneth Westover 👨🔬
Affiliation: Department of Radiation Oncology, UT Southwestern Medical Center, University of Texas Southwestern Medical Center, UT Southwestern Medical Center, RefleXion Medical 🌍
Purpose: Biology-guided radiotherapy (BgRT) is a novel FDA-cleared technology for treating lung and bone tumors based on 18F-FDG PET uptake. This study summarizes the first-year experience treating 29 potential BgRT candidates using the RefleXion X1 PET-linac platform between November 2023 and December 2024.
Methods:
Patients with PET-avid lung or bone tumors were evaluated based on inclusion criteria such as SUV uptake, tumor size, and prescription dose (Rx). Functional-modeling PET and treatment PET data were acquired on the RefleXion X1 system following a 15 mCi FDG injection and ~60-minute uptake period. Functional PET images were used to create BgRT plans, and treatments were guided by real-time PET imaging. IMRT QA verified dosimetric accuracy.
Results: Of 29 patients evaluated, 23 underwent PET modeling, and 17 proceeded with BgRT treatments (10 lung, 7 bone tumors), delivering 48 fractions. Fifteen patients completed treatment. Prescriptions ranged from 7–28 Gy/fraction for a total of 1–5 fractions. Most plans achieved 100% prescription coverage of 95% PTV while adhering to OAR constraints, with conformity indices (CI) ranging from 1.1 to 1.4. The average FDG injection dose was 14.9 mCi, meeting activity concentration (AC) thresholds (>5 kBq/mL) and normalized target signal (NTS) thresholds (>2). For most patients, AC and NTS demonstrated downward trends during treatment. Notably, one case exhibited a 77% reduction in tumor volume and PET uptake, triggering an offline adaptation process. Average patient preparation and uptake time was 95 minutes, in-vault time was 79 minutes, and total departmental time was 203 minutes. All QA plans passed, with ionization chamber-measured point dose errors <5% and 90% Gamma passing rates using 2%/2 mm criteria
Conclusion: This study represents the first large-scale clinical evaluation of BgRT in an academic setting. Clinical outcomes and key findings from these BgRT cases are under investigation as part of an ongoing clinical trial