Evaluation of OAR Sparing and Influence on a Next-Generation Bgrt Platform
Abstract
Purpose
For BgRT treatment on the RefleXion X1 linac, patients must meet stringent criteria regarding the proximity and 18F-FDG activity of OARs near the target. The next-generation X2 platform has an increased PET field of view, and new planning, PET detection, and target tracking algorithms are in development. We sought to investigate the new system’s ability to spare OARs close to the BgRT target, as well as delivery robustness against interference from FDG-avid OARs.
Methods
We performed six OAR-related phantom tests on X2 systems. Two tests explored the developmental X2’s ability to carve dose away from a virtual, non-FDG-avid (“cold”) OAR located 1 cm from a static or moving BgRT target. The other tests involved FDG-avid (“hot”) volumes of various activity and relative distance to the static or moving BgRT target, to simulate the impact of “hot” OARs on target tracking and dose delivery.
Results
In the “cold” OAR tests, the X2 system generated conformal treatment plans which satisfied dosimetric constraints for the virtual OAR structure near the BgRT target. Ion-chamber point-dose measurements agreed within 2% and phantom array gamma passing rates were > 96% (3%/2mm), confirming delivery spared the virtual OAR. In the “hot” OAR tests, the X2 system was able to generate and deliver conformal plans even with the OAR encroaching on or slightly into the target tracking region. Ion-chamber point-dose and film measurements confirmed clinically satisfactory delivery, with point doses within 3% of planned doses.
Conclusion
We performed a suite of phantom tests to investigate the capabilities of the next-generation RefleXion X2 system regarding OAR sparing and OAR influence on BgRT treatment plan preparation and delivery. The system was able to generate clinically satisfactory plans which exhibited very good conformality and robust target tracking at delivery despite OAR constraints; this could increase patient eligibility for BgRT.