Does the Pretherapeutic Tumor SUV in 68Ga DOTATOC PET Predict the Absorbed Dose of 177Lu Octreotate?

Purpose: Selection of candidates for peptide receptor radionuclide therapy (PRRT) is increasingly based on receptor positron emission tomography (PET) imaging, including the common tracer Ga-68 DOTATOC. However, no studies have yet compared standardized uptake values (SUVs) and absorbed doses in this field. Materials and Methods: We retrospectively analyzed a consecutive cohort of 21 patients with 61 evaluable tumor lesions undergoing both pretherapeutic Ga-68 DOTATOC-PET/CT (Biograph Duo [Siemens Medical Solutions, Erlangen, Germany]; PET acquisition, 75.3 +/- 15.4 minutes postinjection; 117.3 + 33.9 MBq Ga-68 DOTATOC) and PRRT with Lu-177 octreotate (7.47 +/- 1.39 GBq; intratherapeutic tumor dosimetry with serial whole-body scans; 1, 2, and 4 days postinjection) at our institution. SUVs were compared with the tumor-absorbed doses per injected activity (D/A(0)) of the subsequent first treatment cycle. Results: The correlation of SUV and D/A(0) was r = 0.72 (SUVmean) and r = 0.71 (SUVmax), both P < 0.001. Pancreatic origin and hepatic localization were associated with higher D/A(0), and chromogranin A level and Ki-67 index had no influence on SUV or D/A(0). High-SUV lesions (SUVmean > 15; SUVmax >25) resulted in high D/A(0) (>10 Gy/GBq) in 66.7% to 70.8% and low D/A(0) (<5 Gy/GBq) in only 8.3% to 12.5% on subsequent PRRT. The mentioned low D/A0 range, on the other hand, was achieved by all lesions with SUVmean <7 or SUVmax <9. Conclusions: Somatostatin receptor PET imaging may predict tumor-absorbed doses. The ability to indicate insufficient target irradiation by a low SUV could aid in selection of appropriate candidates for PRRT. However, larger series are needed to confirm and validate these initial findings.