Abstract
1184
Objectives Selection of candidates for peptide receptor radionuclide therapy (PRRT) is increasingly based on receptor PET imaging, including the common tracer 68Ga- DOTATOC. However, no studies have yet compared SUV and absorbed doses in this field.
Methods We retrospectively analyzed a consecutive cohort of 21 patients with n=61 evaluable tumor lesions undergoing both pre-therapeutic 68Ga-DOTATOC-PET-CT (Biograph Duo; PET acquisition 75.3 ± 15.4 min p.i.; 117.3 ±33.9 MBq 68Ga-DOTATOC) and PRRT with 177Lu-octreotate (7.47 ±1.39 GBq; intratherapeutic tumor dosimetry with serial whole-body scans; 1, 2 and 4 d p.i.) at our institution. SUV values were compared with the tumor-absorbed doses per injected activity (D/A0) of the subsequent first treatment cycle.
Results The correlation of SUV and D/A0 was r= 0.72 (SUVmean) and r= 0.71 (SUVmax), both p<0.001. Pancreatic origin and hepatic localisation were associated with higher D/A0, chromogranin A level and Ki-67 index had no influence on SUV or D/A0. High-SUV lesions (SUVmean> 15; SUVmax> 25) resulted in high D/A0 (> 10 Gy/GBq) in 66.7- 70.8%, and low D/A0 (< 5 Gy/GBq) in only 8.3-12.5% 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 to some extent 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 these initial findings