A comparison of 68Gallium-DOTA-TOC and 18F-FDG PET/CT in imaging of neuroendocrine tumors (NETs)

Objectives Our purpose was to compare the performance of 68Ga-1,4,7, 10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid-D-Phe1,Tyr3-octreotide (DOTA-TOC), a novel selective somatostatin receptor 2 PET ligand, and 18F-FDG in the detection of NETs using PET/CT with emphasis on the following aspects-staging, restaging, monitoring response to therapy, prediction of prognosis, selection of appropriate therapy and establish a possible relationship between SSTR and glucose metabolic status.

Methods Ninety patients (50men,40women;mean age 42.5 yrs) underwent the above two imaging studies. Study population was divided into two groups. The first group comprised of patients (n=48) who were already treated and had histopathological confirmation of their diagnosis, while the other group (n=42) was referred for detection of unknown primary NET (CUP-NET).

Results Results of 18F-FDG were reported as positive in 41 patients. Mean SUVmax of the lesions were 3.42. 68Ga-DOTA-TOC PET/CT was reported as positive in 76 cases with a mean SUvmax of 9.0, an overall higher lesion detection rate and sensitivity compared to 18F-FDG PET/CT (95% Vs 53%).

Conclusions Although 68Ga-DOTA-TOC PET/CT performed better than 18F-FDG PET/CT, the implication of both studies are different. 68Ga-DOTATOC PET/CT was superior in localizing the primary tumor and for restaging purpose while 18F-FDG PET/CT revealed information which were more important from therapeutic point of view and determination of prognosis ( a higher FDG uptake portends a poor prognosis).Further there is a possible inverse relationship between SSTR and glucose metabolic status(SSTR expression is a feature of well-differentiated tumor while FDG uptake is a marker of anaplasia)