Gastroenteropancreatic neuroendocrine tumors: standardizing therapy monitoring with 68Ga-DOTATOC PET/CT using the example of somatostatin receptor radionuclide therapy.

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 68Ga-DOTATOC PET/CT were compared before and after the last SRRT. On 68Ga-DOTATOC PET/CT, the maximum standard uptake values (SUVmax) 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 (SUVmax of the normal liver plus 10% [VOIliver+10%], 20% [VOIliver+20%], 30% [VOIliver+30%] and SUV  =  10 [VOI10SUV]). The SUVmax 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), ΔSUVmax  =  -22 (-29 to-14), and ΔVOI10SUV  =  -53 (-68 to -38)% and significant with p < .05 for ΔVOIliver+10%  =  -29 (-55 to -3)%, ΔVOIliver+20%  =  -32 (-62 to -2) and ΔVOIliver+30%  =  -37 (-66 to -8). Correlations were found only between ΔCgA and ΔVOI10SUV (r  =  .595; p < .01), ΔSUVmax and ΔVOI10SUV (0.629, p < .01), and SUVmax and ΔSUVmax (r  =  -.446; p < .05). 68Ga-DOTATOC PET/CT allows volumetric therapy monitoring via an SUV-based cut-off separating hepatic metastases from normal liver tissue (10 SUV recommended).