Comparison of [111In]octreotide scintigraphy and [68Ga]DOTATOC PET in GEP-NETs: concordance of Krenning scores and implications for PRRT treatment eligibility

Background: Peptide receptor radionuclide therapy (PRRT) is an established treatment for somatostatin receptor (SSTR)-positive gastroenteropancreatic neuroendocrine tumors (GEP-NETs), with eligibility determined by the Krenning score. While SSTR PET provides greater sensitivity than octreotide scintigraphy, its impact on PRRT eligibility remains unclear. We compared Krenning scores between [111In]octreotide scintigraphy and [68Ga]DOTATOC PET and assessed eligibility under NETTER-1 and NETTER-2 criteria. Methods: We retrospectively assessed tumor Krenning scores in 115 patients with well-differentiated GEP-NETs who underwent both [111In]octreotide scintigraphy and [68Ga]DOTATOC PET. PRRT eligibility was defined according to NETTER-1 (Krenning ≥2) and NETTER-2 (Krenning ≥3) criteria. Logistic regression identified predictors of Krenning ≥3 on SSTR PET. Quantitative PET analysis was performed for patients with positive baseline [68Ga]DOTATOC PET scans. Results: Median Krenning scores were higher with SSTR PET than planar imaging (3 [IQR 3-4] vs. 2 [IQR 0-3], P<10-8). NETTER-1 eligibility increased from 59.1% with planar imaging to 81.7% with PET (P<10-3), and NETTER-2 from 48.7% to 76.5% (P<10-4). Among patients eligible on planar imaging, 95.6% (NETTER-1) and 98.2% (NETTER-2) had concordant PET findings. Conversely, 61.7% (NETTER-1) and 55.9% (NETTER-2) of patients ineligible on planar imaging were reclassified as eligible with PET. Metastatic disease was associated with higher SSTR PET uptake (OR 9.5 [95%CI 2.7-32.8], P<10-3). SUVmax discriminated patients with Krenning ≥3 using an optimal threshold of 9.2 (AUC 0.93). Conclusions: [68Ga]DOTATOC PET yields higher Krenning scores and increases PRRT eligibility compared with [111In]octreotide scintigraphy. PET may be unnecessary for clearly positive planar studies but identifies additional candidates with borderline or negative planar results.