Author: Jon Burns, Andrew Groll, Gopinath Kuduvalli, Thomas Laurence, Manoj Narayanan, Jeffrey Schmall, Sanchit Sharma π¨βπ¬
Affiliation: RefleXion Medical π
Purpose: To simplify BgRT testing we have developed techniques that use 3D resin printed structures that can be filled with Ge-68 epoxy. This approach allows the development of highly complex, clinically relevant targets, with prolonged use (271-day half-life), and a simplification of phantom preparation eased by the removal of liquid sources. Here we share the design and initial characterization of these Ge-68 filled targets, demonstrate their use in BgRT characterization studies, and show their equivalence to FDG-filled phantoms.
Methods: The activity concentration of the Ge-68 epoxy was chosen as 40kBq/ml to represent lesions at ~8:1 uptake contrast ratio in the presence of a 5 kBq/ml background. Characterization of the targetβs uniformity and concentration was performed using a dose calibrator and the RefleXion-X1 PET-CT subsystem, respectively. RT plans were developed with the Ge-68 filled targets in both cold and hot background (5kBq/ml), and with FDG-only filled phantoms for comparison. BgRT delivery accuracy was assessed using a combination of ArcCHECK SNC gamma, ion-chamber (IC) readings, and Ashland EBT-XD film measurements.
Results: kVCT and PET image data verified high-uniformity of the Ge-68 epoxy. SCINTIX plans were developed using the Ge-68 targets and the resulting AC and normalized target signal (NTS) values were 16.0kBq/ml and 53.5, respectively. SCINTIX plans using the Ge-68 targets in a ~5 kBq/ml FDG background solution had AC and NTS values of 13.4kBq/ml and 16.3, respectively. These values match well to studies using FDG-filled targets. Delivered dosimetry measurements of SCINTIX plans with the Ge-68 targets achieved SNC gamma of 96.5% (3%,2mm), IC error of 1.8%, and film PTV gamma (3%,3mm) of 97.4%. Collectively these results match well to results obtains with FDG-only filled phantoms.
Conclusion: We demonstrate that this approach can yield accurate activity concentrations with high-uniformity and achieve similar performance to FDG-filled phantoms when used for SCINITIX therapy.