The effect of eating on the uptake of PSMA ligands in the salivary glands

RATIONALE: PSMA-directed therapy for metastatic prostate cancer is gaining adoption as a treatment option. However, accumulation of (177)Lu/(225)Ac-PSMA in the salivary glands remains a problem, with risk of dose-limiting xerostomia and potentially severe effect on the quality of life. Gustatory stimulation is an approach that has commonly been used in radioactive iodine therapy to reduce accumulation in the salivary glands. However, based on theoretical differences in biodistribution, it was hypothesized that this could potentially lead to adverse increased toxicity for PSMA-ligand therapy. The primary objective of this work was to determine if gustatory stimulation by eating an assortment of sweet/fatty/acidic foods during the biodistribution phase of [(18)F]DCFPyl could result in a clinically relevant (> 30%) change in the uptake of the tracer in the salivary glands. METHODS: 10 patients who already received a whole-body [(18)F]DCFPyl PET/CT scan for evaluation of prostate cancer, underwent a repeat (intervention) PET/CT scan within a month of the first (control) scan. During the intervention scan, patients chose from an assortment of sweet/fatty/acidic foods, which they then chewed and swallowed for a period of time starting 1 min before tracer administration to 10 min thereafter. Data from both scans were analyzed by placing VOIs on the major salivary glands and segmenting them using relative thresholds. RESULTS: A slight increase in PSMA uptake in the parotid glands was observed on the intervention scan when compared to the baseline scan (+ 7.1% SUL(mean) and + 9.2% SUL(max), p < 0.05). No significant difference in PSMA uptake in the submandibular glands was seen. CONCLUSIONS: Eating only slightly increases uptake of [(18)F]DCFPyl in the parotid glands. We nonetheless recommend refraining from gustatory stimulation during the administration and early biodistribution phase of radionuclide therapy with PSMA-ligands to reduce the risk of avoidable additional toxicity. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13550-021-00838-y.