Abstract
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.ResultsIn patients with high tumor load, SUVmean 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 (p < 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 (p < 0.05). SUV in lacrimal, salivary glands and kidneys correlated negatively with PSA.Materials and Methods135 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.ConclusionsPatients 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.
Highlights
The prostate-specific membrane antigen (PSMA) is a promising target for prostate cancer diagnostics and therapy
In patients with high tumor load, SUVmean 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 (p < 0.001)
Total tracer retention was higher in patients with high tumor load (p < 0.05)
Summary
The prostate-specific membrane antigen (PSMA) is a promising target for prostate cancer diagnostics and therapy. Accumulation of PSMA-ligands is observed in non-tumorous normal tissues, such as liver, spleen, kidneys and salivary glands. The total tumor mass might affect uptake in doselimiting normal organs due to a tumor steal effect. It is currently unknown if a tumor steal effect is applicable to PSMA-targeting radiotracers and to what extent it affects the biodistribution of the radiopharmaceutical in normal tissues. Knowledge of these effects is fundamental for estimation of maximum tolerated activities and optimization of clinical radionuclide therapy protocols
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