Uptake of PSMA-ligands in normal tissues is dependent on tumor load in patients with prostate cancer.

Unlabelled: Radioligand therapy (RLT) with Lu-177-labeled PSMA-ligands is a new therapy option for prostate cancer. Biodistribution in normal tissues is of interest for therapy planning. We evaluated if the biodistribution of Ga-68-PSMA-11 is influenced by tumor load.

Results: In patients with high tumor load, SUV was reduced to 61.5% in the lacrimal glands, to 56.6% in the parotid glands, to 63.7% in the submandibular glands, to 61.3% in the sublingual glands and to 55.4% in the kidneys ( < 0.001). Further significant differences were observed for brain, mediastinum, liver, spleen and muscle. Total tracer retention was higher in patients with high tumor load ( < 0.05). SUV in lacrimal, salivary glands and kidneys correlated negatively with PSA.

Materials And Methods: 135 patients were retrospectively evaluated. SUV was measured in the lacrimal and salivary glands, brain, heart, liver, spleen, kidneys, muscle and bone. SUV was correlated with visual tumor load, total tracer retention and PSA.

Conclusions: Patients with high tumor load show a significant reduction of tracer uptake in dose-limiting organs. As similar effects might occur when performing RLT using Lu-177-labeled PSMA-ligands, individual adaptations of therapy protocols based on diagnostic PSMA PET imaging before therapy might help to further increase efficacy and safety of RLT.