Pre-Clinical Evaluation of a Next-Generation PET-Based Biology-Guided Radiotherapy Platform for Targets with Inhomogeneous Tracer Avidity
Abstract
Purpose
The next-generation PET-based SCINTIX® Biology-guided radiotherapy (BgRT) X2 platform incorporates a four-time PET widened field of view (WFOV) and an anchor-point-tracking delivery algorithm (currently in development). These advancements are intended to improve biological signal sensitivity, workflow efficiency, and delivery robustness compared to the X1 platform, particularly for targets with heterogeneous radiotracer uptake. In this study, we perform a pre-clinical, phantom-based evaluation of the next-generation platform, focusing on scenarios with markedly inhomogeneous tracer avidity.
Methods
Static ArcCHECK phantom experiments were performed with customized inserts containing one or two spherical targets. Four configurations simulated heterogeneous tracer-uptake inside a 7cm length PTV: (1) a single 22mm-diameter Ge-68-filled-sphere (22mm-Ge-sphere) without background activity; (2) a single 22mm-diameter FDG-filled-sphere (22mm-FDG-sphere) with a 10:1 target-to-background ratio (TBR) ; (3) two 22mm-Ge-spheres with a 20:1 TBR; and (4) a single 15mm-FDG-sphere for the planning PET scan that was replaced with a 22mm-FDG-sphere during delivery. The SCINTIX-specific planning-target-volume (PTV) was generated by expanding the tracer-avid volume (GTV) to form a PTV with a length of 7cm. Four BgRT plans (10Gy/fraction) were generated and delivered. Pre-treatment PET metrics including activity concentration (AC), normalized target signal (NTS), and bounded dose-volume-histogram (bDVH) were recorded. Delivered dose distributions were analyzed and compared with ArcCHECK measured via gamma analysis at 3%/3mm.
Results
All experiments showed heterogeneous tracer distribution in the PTV. PET metrics confirmed adequate biological signal (100% bDVH coverage) across all cases. Delivered and planned dose distributions showed excellent agreement for all X2 cases (gamma-passing-rate >99%), while X1 is constrained by treatable tumor length (≤5cm) and separation from the PET-avid region edge to the PTV edge (≤2cm).
Conclusion
The next-generation SCINTIX X2 platform demonstrates accurate and robust BgRT delivery for targets with substantial tracer heterogeneity, notably expanding the treatable biological target geometries compared with the current clinical X1 system.