Abstract
BACKGROUND: Retrospective and small prospective studies of [(177)Lu]Lu-DOTATATE treatment suggest clinical activity in meningioma. Frequently, pretherapeutic SSTR expression as determined by SSTR PET is used to evaluate eligibility for such therapies, although threshold definitions are manifold and poorly validated. This study aims at comparing the frequency of [(18)F]SiTATE positivity using commonly applied thresholds. METHODS: In this retrospective study, patients with [(18)F]SiTATE PET at recurrence of meningioma were included. SSTR+ definitions were based on threshold-based assessments including absolute thresholds (SUV(max)>2.3, SUV(max)>4.0, SUV(max)>10, SUV(mean)>4.0), as well as SUV(max) relative to reference regions such as the pituitary gland (SUVR(pit)>0.3), the superior sagittal sinus (SUVR(SSS)>3.2), and normal brain parenchyma (SUVR(norm)>62.6). Visual assessment was used as reference, and accuracy, sensitivity, as well as specificity were calculated and compared. RESULTS: In total, 211 patients (130 [61.6%] females) at a median age of 60 years (range: 24-85) were included, and 431 lesions (median 1 lesion per patient [range: 1-9]) were evaluated. Tumor locations were the parasagittal region in 108/431 (25.1%), the cerebral convexity in 82/431, 19.0%), and the sphenoid wing in 54/431 (12.5%) lesions. By visual assessment, 399/431 (92.6%) lesions were defined as SSTR+. Using absolute SUV thresholds, SSTR+ meningiomas were 419/431 (97.2%) for SUV(max)>2.3, 344/431 (79.8%) for SUV(max)>4, 139/431 (32.3%) for SUV(max)>10, and 342/431 (79.4%) for SUV(mean)>4. Applying thresholds relative to reference regions, 328/431 (76.1%) were SSTR+ at SURV(SSS)>3.2, 226/431 (52.4%) at SUVR(pit)>0.3, and 95/431 (22.0%) at SUVR(norm)>62.6. The highest concordance of these definitions with visual assessment was observed for SUV(max)>2.3 (accuracy: 92.6%; sensitivity: 98.5%; specificity: 18.8%), followed by SUV(max)>4 (accuracy: 87.2%; sensitivity: 86.2%; specificity: 100.0%). CONCLUSION: SUV(max)>2.3 and SUV(max)>4 showed the highest concordance with visual assessment for SSTR+ definition. While SUV(max)>10 is a frequently used inclusion criterion for radioligand therapy trials, only a relatively small fraction of meningiomas meets this threshold. Validated reader-independent definitions are needed to guide the design of future clinical trials on SSTR-targeted radioligand therapies in meningioma.