PSMA PET/CT Identifies Intrapatient Variation in Salivary Gland Toxicity From Iodine-131 Therapy

Xerostomia is a well-known complication after iodine-131 (¹³¹I) therapy for thyroid carcinoma. It is currently insufficiently understood how the dose and biodistribution of ¹³¹I relates to salivary gland toxicity, and whether this is consistent for all salivary glands within a single patient. Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) was recently introduced as a new tool to evaluate the relative loss of vital acinar cells in individual salivary glands. We aimed to assess gland-specific salivary gland toxicity after ¹³¹I-therapy using PSMA PET/CT.

Five patients with differentiated thyroid cancer underwent [⁶⁸Ga]Ga-PSMA-11 PET/CT to evaluate their eligibility for peptide radioligand therapy with [¹⁷⁷Lu]Lu-PSMA-617. Uptake patterns in salivary glands were evaluated visually and quantitatively as an indicator of vital acinar cell loss after prior ¹³¹I-therapy.

Four of 5 patients demonstrated significant lowered uptake in at least one salivary gland, after receiving at least 2 ¹³¹I-treatments. Asymmetric loss of vital acinar cells occurred by gland type (parotid/submandibular) and location (right/left). The other salivary glands in these patients and all salivary glands in the fifth patient showed normal uptake, demonstrating high intrapatient and interpatient variability.

¹³¹I-therapy can induce salivary gland toxicity with high inter- but also high intrapatient variation among separate gland locations, which can be assessed with PSMA PET/CT. This new technique offers potential to guide further development and evaluation of protective measures in patients receiving ¹³¹I-therapy.