Salivary scintigraphy as a pre-treatment diagnostic tool to predict gland dysfunction following 131I therapy.

Objective: To evaluate whether pre-treatment salivary gland scintigraphy (SGS) with technetium-99m pertechnetate (^99mTcO₄^-) can predict the risk of moderate to severe salivary gland dysfunction and xerostomia in differentiated thyroid cancer (DTC) patients following their first radioiodine-131 (¹³¹I) therapy.

Subjects and methods: We retrospectively enrolled 149 DTC patients (107 females, 42 males; mean age 46.6±12.7 years) who underwent total thyroidectomy between October 2022 and March 2024. All subjects received pre-treatment SGS to measure the uptake index (UI) and excretion fraction (EF) of bilateral parotid and submandibular glands. Patients then underwent ¹³¹I therapy (1.85-5.55GBq) and repeat SGS 6-12 months later under identical conditions. Xerostomia severity was assessed using the xerostomia inventory (XI) score, categorizing patients into no/mild (XI 11-23) versus moderate-extreme xerostomia (XI 24-55).

Results: Post-therapy, all glands exhibited significant declines in UI (parotid and submandibular glands, P<0.001) and EF (P≤0.004). There was no significant correlation between administered ¹³¹I dose and percentage changes in UI (ΔUI%) or EF (ΔEF). However, higher ¹³¹I doses were associated with increased rates of moderate-severe xerostomia (P=0.015) and higher mean XI scores (P=0.008). Receiver operating characteristic (ROC) analysis demonstrated that pre-treatment UI reliably predicted moderate to severe functional decline (ΔUI% >20%) with areas under the curve (AUC) of 0.866 for the right parotid, 0.793 for the left parotid, 0.769 for the right submandibular, and 0.816 for the left submandibular glands (all P<0.001). Additionally, ΔUI% in both submandibular glands differed significantly between patients with no/mild and moderate-extreme xerostomia (right: P=0.004; left: P=0.012).

Conclusion: Pretreatment ^99mTcO₄^- SGS uptake index is a dependable predictor of moderate to severe salivary gland dysfunction and xerostomia following ¹³¹I therapy in DTC patients, enabling early identification of individuals at high risk and guiding tailored preventive strategies.