Inflammation-Based Index and 68Ga-DOTATOC PET–Derived Uptake and Volumetric Parameters Predict Outcome in Neuroendocrine Tumor Patients Treated with 90Y-DOTATOC

We performed post hoc analyses on the utility of pretherapeutic and early interim Ga-68-DOTATOC PET tumor uptake and volumetric parameters and a recently proposed biomarker, the inflammation-based index (IBI), for peptide receptor radionuclide therapy (PRRT) in neuroendocrine tumor (NET) patients treated with Y-30-DOTATOC in the setting of a prospective phase II trial. Methods: Forty-three NET patients received up to 4 cycles of Y-90-DOTATOC at 1.85 GBq/m(2)/cycle with a maximal kidney biologic effective dose of 37 Gy. All patients underwent Ga-68-DOTATOC PET/CT at baseline and 7 wk after the first PRRT cycle. Ga-68-DOTATOC-avid tumor lesions were semiautomatically delineated using a customized SUV threshold- based approach. PRRT response was assessed on CT using RECIST 1.1. Results: Median progression-free survival and overall survival (OS) were 13.9 and 22.3 mo, respectively. An SUVmean higher than 13.7 (75th percentile) was associated with better survival (hazard ratio [HR], 0.45; P = 0.024), whereas a Ga-68-DOTATOC- avid tumor volume higher than 578 cm(3) (75th percentile) was associated with worse OS (HR, 2.18; P = 0.037). Elevated baseline IBI was associated with worse OS (HR, 3.90; P = 0.001). Multivariate analysis corroborated independent associations between OS and SUVmean = 0.016) and IBI (P = 0.015). No significant correlations with progression-free survival were found. A composite score based on SUVmean and IBI allowed us to further stratify patients into 3 categories with significantly different survival. On early interim PET, a decrease in SUV mean of more than 17% (75th percentile) was associated with worse survival (HR, 2.29; P = 0.024). Conclusion: Normal baseline IBI and high Ga-68-DOTATOC tumor uptake predict better outcome in NET patients treated with Y-30-DOTATOC. This method can be used for treatment personalization. Interim Ga-68-DOTATOC PET does not provide information for treatment personalization.