Evaluating the biodistribution for [Ga]Ga-PSMA-11 and [F]F-PSMA-1007 PET/CT with an inter- and intrapatient based analysis.

BACKGROUND

Liver uptake in [Ga]Ga-PSMA-11 PET is used as an internal reference in addition to clinical parameters to select patients for [Lu]Lu-PSMA-617 radioligand therapy (RLT). Due to increased demand, [Ga]Ga-PSMA-11 was replaced by [F]F-PSMA-1007, a more lipophilic tracer with different biodistribution and splenic uptake was suggested as a new internal reference. We compared the intra-patient tracer distribution between [Ga]Ga-PSMA-11 and [F]F-PSMA-1007.

METHODS

Fifty patients who underwent PET examinations in two centers with both [F]F-PSMA-1007 and [Ga]Ga-PSMA-11 within one year were included. Mean standardized uptake values (SUV) were obtained for liver, spleen, salivary glands, blood pool, and bone. Primary tumor, local recurrence, lymph node, bone or visceral metastasis were also assessed for intra- and inter-individual comparison.

RESULTS

Liver SUV was significantly higher with [F]F-PSMA-1007 (11.7 ± 3.9) compared to [Ga]Ga-PSMA-11 (5.4 ± 1.7, p < .05) as well as splenic SUV (11.2 ± 3.5 vs.8.1 ± 3.5, p < .05). The blood pool was comparable between the two scans. Malignant lesions did not show higher SUV on [F]F-PSMA-1007. Intra-individual comparison of liver uptake between the two scans showed a linear association for liver uptake with SUV [Ga]Ga-PSMA-11 = 0.33 x SUV [F]F-PSMA-1007 + 1.52 (r = .78, p < .001).

CONCLUSION

Comparing biodistribution of [Ga]Ga and [F]F tracers, liver uptake on [Ga]Ga-PSMA-11 PET is the most robust internal reference value. Liver uptake of [F]F-PSMA-1007 was significantly higher, but so was the splenic uptake. The strong intra-individual association of hepatic accumulation between the two scans may allow using of a conversion factor for [F]F-PSMA-1007 as a basis for RLT selection.