JS03.6.A COMPARISON OF [18F]SITATE PET POSITIVITY DEFINITIONS AS ELIGIBILITY CRITERION FOR SOMATOSTATIN RECEPTOR-TARGETED RADIOLIGAND THERAPIES

Abstract BACKGROUND Clinical trials evaluating [177Lu]Lu-DOTATATE treatment in meningioma are ongoing. While somatostatin receptor (SSTR) expression is used as inclusion criterion, definitions of SSTR-positivity (SSTR+) in PET are manifold and poorly validated. This study aims at comparing the frequency of PET-positivity using commonly used thresholds reported in the literature. MATERIAL AND METHODS Patients with recurrent meningioma who underwent [18F]SiTATE PET were included. SSTR+ definitions were based on visual and threshold-based assessments including SUVmax>2.3, SUVmax>4.0, SUVmax>10, SUVmean>4.0, as well as SUVmax relative to reference regions such as the pituitary gland (SUVRpit>0.3), the superior sagittal sinus (SUVRSSS>3.2), and normal brain parenchyma (SUVRnorm>62.6). For comparative analyses, visual assessment was used as reference, and accuracy, sensitivity, as well as specificity were calculated accordingly and compared between SSTR+ definitions. RESULTS Overall, 211 patients (130 [61.6%] females; median age: 60 years [range: 24-85]) with 431 lesions (median 1 lesion per patient [range: 1-9]) were included. Most meningiomas were parasagittal (108/431, 25.1%), followed by those located at the cerebral convexity (82/431, 19.0%) and sphenoidal meningiomas (54/431, 12.5%). Visually, 399/431 (92.6%) lesions were deemed SSTR+. Using absolute SUV thresholds, 419/431 (97.2%) were defined as SSTR+ at SUVmax>2.3, 344/431 (79.8%) at SUVmax>4, 139/431 (32.3%) at SUVmax>10, and 342/431 (79.4%) at SUVmean>4. Applying thresholds relative to reference regions, 328/431 (76.1%) were SSTR+ at SUVRSSS>3.2, 226/431 (52.4%) at SUVRpit>0.3, and 95/431 (22.0%) at SUVRnorm>62.6. Visual assessment showed the highest concordance with SUVmax>2.3 (accuracy: 92.6%; sensitivity: 98.5%; specificity: 18.8%), followed by SUVmax>4 (accuracy: 87.2%; sensitivity: 86.2%; specificity: 100.0%). CONCLUSION Visual assessment shows high concordance with SUVmax>2.3 and SUVmax>4. Importantly, only a fraction of included meningiomas is SSTR+ at SUVmax>10 which represents a frequently used eligibility criterion in radioligand therapy trials. Given the need for reader-independent definitions, these results could inform the design of future clinical trials on SSTR-targeted radioligand therapies in meningioma.