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Location: Marriott Marquis
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PQA 02 - PQA 02 Physics Poster Q&A

2447 - Commissioning of the Reflexion Positron Emission Tomography Guided Radiation Planning and Delivery System

Sunday, September 29, 2024
4:45 PM – 6:00 PM ET
Location: Hall C

Screen: 13

W. T. Watkins1, C. Han1, T. Ketcherside1, Z. Wang1, B. Liu1, K. Qing1, J. Zhu1, Y. Suh1, C. Shi2, and A. Liu1; 1Department of Radiation Oncology, City of Hope National Medical Center, Duarte, CA, 2Department of Radiation Oncology, City of Hope, Irvine, CA

Purpose/Objective(s): The Reflexion Biology Guided Radiation Therapy (BGRT) (Reflexion Medical Systems, Hayward CA) system incorporates Positron Emission Tomography (PET) in treatment planning and delivery. This work details our institutional commissioning of the system for patient treatment. Materials/

Methods: The manufacturer provided custom insert phantoms for the technology company check device including a hollow 2-cm sphere fillable with Fludeoxyglucose F18 (FDG) with a film plane and a point geometry Na-22 source. We constructed custom phantoms composed of solid water, cork to represent lung density, and PET sources including a Ge-68 bar source various cylindrical plastic inserts for FDG filling (diameters 2.2 cm, 3.5 cm, and 5.5 cm). Computed Tomography (CT) and PET Images of the phantoms were acquired on diagnostic PET/CT and on the Reflexion system on a motion platform capable of simulating respiratory motion and intra-fraction gross anatomic shifts. Treatment plans were generated including varying PTV size for fixed PET-source geometry (range 17-230 cc), varying doses from 7-12 Gy / fraction, and varying geometry of proximal PET active regions and background activity. We evaluated the delivery system response in planning conditions, and the system response to perturbations from the planning conditions including varying PET activity and geometric shifts including simulation of respiratory and gross intra-fraction motion.
Results: Varying PTV size and geometry for fixed PET-sources did not affect accurate planning and delivery in planning conditions, confirming BgRT can safely deliver non-uniform margin expansions of PET-active volumes (as is customary in PTV definition). In delivery matching the planning conditions, planned vs. measured dosimetry routinely exceed 90% 3mm/3% Gamma with ion chamber and film readings generally within 3%. Varying PET activity from 30-105% of the planned kBq/ml resulted in no dose variations, indicating the system delivery is robust to injection and uptake variations which may be observed clinically. Geometric variations including varying breathing motion did show interplay effects in large targets reducing Gamma passing rates, but the clinical significance of these variations may be averaged out over several fractions. Intra-fraction geometric shifts of 5-10mm revealed the system has the ability to perform real-time plan adaptation and avoid major dosimetric errors.
Conclusion: The BGRT system was validated as a robust treatment modality for multiple PET sources of varying activity, active volume, and PTVs. When varying delivery parameters, the system was robust against large variations in absolute PET activity and real-time adaptation was possible when gross motion occurred. Further studies are needed to understand the interplay effect in large targets.