We aimed to evaluate 68 Ga-DOTATATE PET/CT for the early prediction of time to progression and clinical outcome after a first cycle of peptide receptor radionuclide treatment (PRRT) in a cohort of patients with well-differentiated neuroendocrine tumors. Methods: Thirty-three consecutive patients (22 men and 11 women; mean age 6 SD, 57.8 6 12.1 y) were investigated at baseline and again 3 mo after initiation of the first cycle of PRRT. 68 Ga-DOTATATE receptor expression was assessed using 2 measures of standardized uptake value (SUV): maximum SUV (SUV max ) and tumor-to-spleen SUV ratio (SUV T/S ). Percentage change in SUV scores after PRRT relative to baseline (DSUV) was calculated. After completing 1-3 cycles of PRRT, patients entered the follow-up study, for estimation of time to progression. According to the Response Evaluation Criteria in Solid Tumors, progression was defined on the basis of contrast-enhanced CT. Clinical symptoms, as well as the tumor markers chromogranin A and neuron-specific enolase, were also recorded during regular follow-up visits. Results: The 23 of 31 patients with decreased SUV T/S after the first PRRT cycle had longer progression-free survival than did the 8 of 31 patients with stable or increased scores (median survival not reached vs. 6 mo, P 5 0.002). For the 18 of 33 patients showing a reduction in SUV max , there was no significant difference in progression-free survival (median survival not reached vs. 14 mo, P 5 0.22). Multivariate regression analysis identified SUV T/S as the only independent predictor for tumor progression during follow-up. In the 17 of 33 patients with clinical symptoms before PRRT, DSUV T/S correlated with clinical improvement (r 5 0.52, P , 0.05), whereas DSUV max did not (r 5 0.42, P 5 0.10). Changes in the tumor markers (chromogranin A and neuronspecific enolase) did not predict DSUV scores, clinical improvement, or time to progression. Conclusion: Decreased 68 Ga-DOTATATE uptake in tumors after the first cycle of PRRT predicted time to progression and correlated with an improvement in clinical symptoms among patients with welldifferentiated neuroendocrine tumors; DSUV T/S was superior to DSUV max for prediction of outcome.

Whole-body bone marrow MRI as used in this study is an effective method for evaluating the entire skeletal system in patients with suspected metastatic disease.

FDG-PET allows for prediction of treatment response by the level of FDG uptake in terms of SUV at baseline and after each cycle of chemotherapy. Moreover, relative changes in SUV after the first and second cycle are a strong predictor of response. Thus, FDG-PET may be helpful for individual treatment stratification in breast cancer patients.

WB-MRI and PET-CT are reliable imaging modalities for tumor staging. WB-MRI is highly sensitive in detecting distant metastases; PET-CT is superior in lymph node staging. PAT makes high-resolution WB-MRI feasible within less than 1 hour.

In this study (68)Ga-DOTA-TATE PET proved clearly superior to (18)F-DOPA PET for detection and staging of NET. (18)F-DOPA uptake tended to be increased in those patients with elevated plasma serotonin. We conclude that (18)F-DOPA PET should be employed in patients with NET with negative (68)Ga-DOTA-TATE PET and elevated plasma serotonin.