Repeatability of gallium-68 DOTATOC positron emission tomographic imaging in neuroendocrine tumors

Abstract

Objective: To evaluate the repeatability of gallium-68 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic (DOTA)-D-Phe1-Try3-octreotide (68Ga-DOTATOC) positron emission tomography (PET) in neuroendocrine tumors.

Methods: Five patients with neuroendocrine tumors were imaged with 68Ga-DOTATOC PET twice within 5 days. Maximum and mean standardized uptake values (SUVmax and SUVmean) and kinetic parameters (K-Patlak and K-influx) of target lesions were measured. The repeatability of these measurements was investigated.

Results: Forty-seven target lesions were identified on whole-body PET and 21 lesions on dynamic images. There was excellent repeatability with intraclass correlation coefficient of 0.99 for SUVmax, SUVmean, and K-Patlak, and 0.85 for K-influx. The median absolute percent differences and the interquartile ranges (IQR) between 2 scans for SUVmax and SUVmean were 7.4% (IQR, 14.1%) and 9.3% (IQR, 10.6%), respectively. The median absolute percent differences for K-Patlak and K-influx were 12.5% (IQR, 12.6%) and 29.9% (IQR, 22.4%), respectively. The SUVmax of target lesions did not differ by more than 25% between the 2 scans.

Conclusions: 68Ga-DOTATOC PET imaging of neuroendocrine tumors is highly reproducible. A difference of more than 25% in SUVmax represents a change that is larger than the measurement error observed on repeated studies and should reflect a significant change in the biological character of the tumor.

Figure 1

(A–E): ⁶⁸Ga-DOTATOC whole body PET (maximum intensity projection; Figure 1A) and select PET-CT images (Figure 1B–E) of a subject with widepread metastatic neuroendocrine tumor. Note the multiple liver lesions (Figure 1B; arrow), thoracic spine lesion (Figure 1C; arrow), paraaortic nodal lesions (Figure 1D; arrow) and an ileal small bowel lesion in the right lower quadrant (Figure 1E; arrow). The ileal primary lesion, which was subsequently confirmed surgically, was not detected prospectively on the ¹¹¹In-Octreotide scan obtained prior to ⁶⁸Ga-DOTATOC study.

Figure 2

(A–D): Comparison of uptake measurements on first and second ⁶⁸Ga-DOTATOC PET scan. There is an excellent correlation between two scans for maxSUV, meanSUV, K-Patlak and K-influx. For presentation purposes, 3 lesions with extremely high uptake are not included in the SUV distribution curves and one lesion is excluded in the K-Patlak and K-influx curves.

Fig. 3

(A–D): Bland Altman graphs for maxSUV and meanSUV (3A and 3B), which show the correlation of the difference of SUV (SUV1-SUV2) and the average of the SUV in two scans. Figures 3C and 3D show the correlation between absolute percent difference in SUV and the average SUV in two scans. The difference in SUV between two scans was higher in tumors with higher uptake (3A and 3B); the percent differences were however independent from the magnitude of SUV (3C and 3D).

Fig. 4

(A–B): Box and whisker plot for absolute percent difference for maxSUV and meanSUV from whole body images (Figure 4A) and for kinetic parameters from dynamic data (Figure 4B). Note the outlier values identified using Tukey outlier test. The highest values for absolute percent differences between two scans after exclusion of outliers were 24.9% for maxSUV, 36.8% for meanSUV, 32.0% for K-Patlak and 57.8% for K-influx.