Clinical feasibility of early scanning after administration of ⁶⁸Ga-DOTATOC

Positron emission tomography (PET)/computed tomography (CT) using ⁶⁸Ga-labeled 1,4,7,10-tetraazacyclododecane-N,N',N″,N‴-tetraacetic acid-D-Phe¹-Tyr³-octreotide (DOTATOC) is usually performed about 1-h post-injection; however, because of rapid blood clearance, the waiting time for scanning could possibly be shortened without affecting diagnostic performance. The purpose of this study was to investigate the feasibility of early scanning at 30 min post-injection.

Thirty-eight patients who underwent DOTATOC-PET/CT were analyzed. After administration of ⁶⁸Ga-DOTATOC, data acquisition was performed twice, at 30-min and 60-min post-injection. The number of known or suspected pathological lesions, and quantitative values of those lesions and physiological uptake were compared. SUV_max, SUV_peak, metabolic tumor volume (MTV), and total lesion uptake (TLU) were calculated as quantitative values of the pathological lesions.

A total of 125 known or suspected pathological lesions were found at both timepoints, with no differences between the two datasets. The SUV_max, SUV_peak, MTV, and TLU were highly reproducible, with Spearman's ρ of 0.983, 0.986, 0.918, and 0.981, respectively. The average percent differences (%DIFF_ave) defined as the differences of the values divided by the value at 1-h post-injection were 11.1% for SUV_max, 8.5% for SUV_peak, 15.1% for MTV, and 20.6% for TLU. Physiological uptake in the two datasets was closely comparable in the pituitary gland (Spearman's ρ = 0.954, %DIFF_ave = 11.0%), liver (0.989, 3.9%), spleen (0.970, 6.3%), adrenal glands (0.879, 13.0%), and pancreatic uncus (0.946, 12.7%).

The diagnostic performance of visual interpretation should be comparable between DOTATOC-PET/CT images obtained at 30-min and 60-min post-injection. Some differences between quantitative values may exist; however, they appear to be minimal.