Dysfunction of the Salivary and Lacrimal Glands After Radioiodine Therapy for Thyroid Cancer: Results of the START Study After 6-Months of Follow-Up

Background: Understanding of changes in salivary and lacrimal gland functions after radioactive iodine therapy (¹³¹I-therapy) remains limited, and, to date, no studies have evaluated dose-response relationships between absorbed dose from ¹³¹I-therapy and dysfunctions of these glands. This study investigates salivary/lacrimal dysfunctions in differentiated thyroid cancer (DTC) patients six months after ¹³¹I-therapy, identifies ¹³¹I-therapy-related risk factors for salivary/lacrimal dysfunctions, and assesses the relationships between ¹³¹I-therapy radiation dose and these dysfunctions. Methods: A cohort study was conducted involving 136 DTC patients treated by ¹³¹I-therapy of whom 44 and 92 patients received 1.1 and 3.7 GBq, respectively. Absorbed dose to the salivary glands was estimated using a dosimetric reconstruction method based on thermoluminescent dosimeter measurements. Salivary and lacrimal functions were assessed at baseline (T0, i.e., immediately before ¹³¹I-therapy) and six months later (T6) using validated questionnaires and salivary samplings, with and without stimulation of the salivary glands. Statistical analyses included descriptive analyses and random-effects multivariate logistic and linear regressions. Results: There was no difference between T0 and T6 in the level of parotid gland pain, nor was there difference in the number of patients with hyposalivation, but there were significantly more patients with dry mouth sensation and dry eyes after therapy compared with baseline. Age, menopause, depression and anxiety symptoms, history of systemic disease, and not taking painkillers in the past three months were found to be significantly associated with salivary or lacrimal disorders. Significant associations were found between ¹³¹I-exposure and salivary disorders adjusted on the previous variables: for example, per 1-Gy increase in mean dose to the salivary glands, odds ratio = 1.43 [CI 1.02 to 2.04] for dry mouth sensation, ß = -0.08 [CI -0.12 to -0.02] mL/min for stimulated saliva flow, and ß = 1.07 [CI 0.42 to 1.71] mmol/L for salivary potassium concentration. Conclusions: This study brings new knowledge on the relationship between the absorbed dose to the salivary glands from ¹³¹I-therapy and salivary/lacrimal dysfunctions in DTC patients six months after ¹³¹I-therapy. Despite the findings of some dysfunctions, the results do not show any obvious clinical disorders after the ¹³¹I-therapy. Nevertheless, this study raises awareness of the risk factors for salivary disorders, and calls for longer follow-up. Clinical Trials Registration: Number NCT04876287 on the public website (ClinicalTrials.gov).