Gastroenteropancreatic Neuroendocrine Tumors: Standardizing Therapy Monitoring with Ga-DOTATOC PET/CT Using the Example of Somatostatin Receptor Radionuclide Therapy

Abstract

The purpose of this study was to standardize therapy monitoring of hepatic metastases from gastroenteropancreatic neuroendocrine tumors (GEP-NETs) during the course of somatostatin receptor radionuclide therapy (SRRT). In 21 consecutive patients with nonresectable hepatic metastases of GEP-NETs, chromogranin A (CgA) and 68 Ga-DOTATOC PET/CT were compared before and after the last SRRT. On 68 Ga-DOTATOC PET/CT, the maximum standard uptake values (SUV max ) of normal liver and hepatic metastases were calculated. In addition, the volumes of hepatic metastases (volume of interest [VOI]) were measured using four cut-offs to separate normal liver tissue from metastases (SUV max of the normal liver plus 10% [VOI liver+10% ], 20% [VOI liver+20% ], 30% [VOI liver+30% ] and SUV = 10 [VOI 10SUV ]). The SUV max of the normal liver was below 10 (7.2 ± 1.3) in all patients and without significant changes. Overall therapy changes (Δ) per patient (mean [95% CI]) were statistically significant with p < .01 for ΔCgA = −43 (−69 to −17), ΔSUV max = −22 (−29 to −14), and ΔVOI 10SUV = −53 (−68 to −38)% and significant with p < .05 for ΔVOI liver+10% = −29 (−55 to −3)%, ΔVOI liver+20% = −32 (−62 to −2) and ΔVOI liver+30% = −37 (−66 to −8). Correlations were found only between ΔCgA and ΔVOI 10SUV ( r = .595; p < .01), ΔSUV max and ΔVOI 10SUV (0.629, p < .01), and SUV max and ΔSUV max ( r = .446; p < .05). 68 Ga-DOTATOC PET/CT allows volumetric therapy monitoring via an SUV-based cut-off separating hepatic metastases from normal liver tissue (10 SUV recommended).