NIMG-14. HEAD-TO-HEAD COMPARISON OF18F-FET PET AND68GA-PSMA-11 PET IN DISTINGUISHING SMALL VOLUME TUMOR PROGRESSION VS TREATMENT-RELATED CHANGE IN POST-STANDARD OF CARE TREATMENT OF HIGH-GRADE GLIOMA USING DYNAMIC ACQUISITION AND KINETIC MODELING

Abstract BACKGROUND The inability to accurately distinguish between tumor progression and treatment-related changes in patients with high-grade glioma on routine imaging can negatively impact patient management and in some cases, outcome. Various imaging methods have been used to address this issue, including 18F-fluoro-ethyl-tyrosine (FET) PET and MR perfusion. However, these methods may not provide reliable results in cases of small lesion size or hemorrhage within the treatment site. The prostate-specific membrane antigen (PSMA) has been observed to be expressed by neovasculature in brain tumors. Since PSMA cannot cross the blood brain barrier, uptake of PSMA in the brain carries high-level of suspicion for residual tumor. Still, further work is needed to better understand PSMA uptake in the tumor bed following standard of care (SOC) treatment and to compare to currently available neuro-oncologic radiotracers, such as FET. We hypothesize that PSMA imaging of glioma neovasculature will provide unique diagnostic information that will aid in the differentiation of small volume tumor progression from treatment-related changes in the post-SOC treatment setting. METHODS Patients who underwent clinical Expanded Access PET/MR imaging with 18F-FET were re-imaged in a research protocol that collected a brain 68Ga-PSMA-11 PET/CT scan, as well as a repeat 18F-FET PET/CT. Kinetic modeling of dynamic radiotracer uptake was performed. Scans were assessed for correlation with subsequent imaging and changes in clinical management. RESULTS All PSMA scans that were performed were concordant with the initial clinical FET scan, subsequent imaging follow up and appropriate changes in clinical management. The PSMA-detected site was confirmed to be tumor in a single case with subsequent tissue sampling. One patient who was started on bevacizumab after their clinical FET demonstrated a significant decrease in uptake on the research FET scan, but persistent uptake on PSMA. CONCLUSION PSMA may effectively show tumor recurrence in post-SOC treatment high-grade glioma patients.