Quantitative SSTR-PET/CT: A Po-tential Tool for Predicting Evero-limus Response in NET Patients

Abstract

Background. This study aimed to assess ⁶⁸Ga-DOTA-TATE (-TOC) PET/CT quantitative parameters in monitoring and predicting everolimus response in neuroendocrine tumor (NET) patients with hepatic metastases (NELM).

Patients and methods. / Materials and methods. This retrospective analysis included 29 patients with 62 target lesions undergoing everolimus treatment and pre-therapy, and follow-up ⁶⁸Ga-DOTA-TATE (-TOC) PET/CT scans. Response evaluation utilized progression-free survival (PFS) categorized as responders (R; PFS > 6 months) and non-responders (NR; PFS ≤ 6 months). Lesion size and density, along with SUV in target lesions, liver, and spleen were assessed. Tumor-to-spleen (T/S) and tumor-to-liver (T/L) ratios were calculated.

Results. PET/CT scans were acquired 19 days (IQ 69 days) pre-treatment and 127 days (IQR 74 days) post-starting everolimus. The overall median PFS was 264 days (95% CI: 134 – 394 days). R exhibited significant decreases in Tmax/Lmax and Tmean/Lmax ratios compared to NR (p=0.01). In univariate Cox regression, Tmean/Lmax ratio was the sole prognostic parameter associated with PFS (HR 0.5, 95% CI 0.28-0.92, p=0.03). Percentage changes in T/L and T/S ratios were significant predictors of PFS, with the highest AUC for the percentage change of Tmean/Lmax (AUC=0.73). An optimal threshold of < 2.5% identified patients with longer PFS (p=0.003). No other imaging or clinical parameters were predictive of PFS.

Conclusions. This study highlights the potential of quantitative SSTR-PET/CT in predicting and monitoring everolimus response in NET patients. Liver metastasis-to-liver parenchyma ratios outperformed size-based criteria, and Tmean/Lmax ratio may serve as a prognostic marker for PFS, warranting larger cohort investigation.