Prognostic Value of Whole-Body PET Volumetric Parameters Extracted from <sup>68</sup>Ga-DOTATOC PET/CT in Well-Differentiated Neuroendocrine Tumors
Philippe Thuillier, Virginia Liberini, Séréna Grimaldi, Osvaldo Rampado, E. Gallio, Bruno De Santi, Emanuela Arvat, Alessandro Piovesan, Roberto Filippi, Ronan Abgral, Filippo Molinari, Désirèe Deandreis
Abstract
<b>Aim:</b> To evaluate the prognostic value of somatostatin receptor tumor burden (SRTB) at <sup>68</sup>Ga-DOTATOC positron emission tomography/computed tomography (PET/CT) in patients with well-differentiated neuroendocrine tumors (WD-NETs). <b>Methods:</b> We retrospectively analyzed <sup>68</sup>Ga-DOTATOC-PET/CT of 84 patients with histologically confirmed WD-NETs (51 G1, 30 G2 and 3 G3). For each PET/CT, all DOTATOC-avid lesions were independently segmented by 2 operators using a customized threshold based on the healthy liver maximum standardized uptake value (SUV<sub>max</sub>) using LIFEx 5.1. Somatostatin receptor expressing tumor volume (SRETV) and total lesion somatostatin receptor expression (TLSRE=SRETV*SUVmean) were extracted for each lesion and then whole-body SRETV and TLSRE (SRETVwb and TLSREwb) were defined as the sum of SRETV and TLSRE of all segmented lesions in each patient, respectively. Time to progression (TTP) was defined as the combination of disease-free-survival in patients undergoing curative surgery (<i>n</i> = 10) and progression-free survival for patients with unresectable/metastatic disease (<i>n</i> = 74). TTP and overall survival (OS) were calculated by Kaplan-Meier analysis, log-rank test, and Cox’s proportional hazard model. <b>Results:</b> After a median follow-up period of 15.5 months disease progression was confirmed in 35 patients (41.7%) and 14 patients died. Higher SRETVwb (>39.1ml) and TLSREwb (>306.8g) were significantly correlated with shorter median TTP (TT<i>P</i> = 12months vs not reached; p<0.001). In multivariate analysis, SRETVwb (<i>P</i> = 0.005) was the only independent predictor of TTP regardless of histopathologic grade and TNM staging. <b>Conclusion:</b> According to our results, SRETVwb and TLSREwb extracted from <sup>68</sup>Ga-DOTATOC-PET/CT could predict TTP/OS and might have an important clinical utility in the management of in patients with WD-NETs.