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Purpose. Quantitative scintigraphy to evaluate salivary gland function changes in patients with differentiated thyroid cancer (DTC) after iodine-131 (131I) treatment. Methods. A total of 458 patients with DTC grouped by sex and age were included. Salivary gland scintigraphy was performed to evaluate salivary gland function before and after 131I treatment. The uptake fraction (UF), uptake index (UI), and excretion fraction (EF) of two pairs of parotid glands and submandibular glands were measured and compared. The Chi-square test was conducted according to function impairment count. Results. Salivary gland function in different age groups and sexes were quite different, especially for women <55 years old, who had decreased UF, UI, and EF of all four glands without basal injury. The secretion or uptake function of some salivary glands with basic function impairment before 131I treatment was increased after iodine treatment. Only a small percentage of males showed reduced functional parameters after several treatments. The most significant difference in the count of impairment for the four salivary glands were the first and third examinations, which was more evident in women. The submandibular gland had the most significant reduction in uptake. Conclusion. Changes in salivary gland function are more common in young females being treated for DTC. Impairment of salivary gland function is correlated with the number of treatments and the cumulative dose of 131I. Some salivary gland functions impaired before 131I treatment were enhanced in the early treatment.

thyroid cancer is excellent. RAI therapy plays an important role in reducing the risk of disease recurrence and tumour-related death, as well as good prognosis. Despite a favourable prognosis, the scope of treatment for many patients with thyroid cancer is controversial, including the extent of surgery as well as the use and dose of RAI therapy [6][7][8]. The side effects of RAI treatment are considered minimal, but RAI may cause some acute or chronic effects [5]. Moreover, the most important concern is whether RAI will benefit survival and increase potential risk of second primary malignancy (SPM) [9,10]. Studies have shown that 19% of patients develop second malignancy after surviving a primary carcinoma [11]. The reasons include continued lifestyle, genetic susceptibility, and treatment modality (radiotherapy and chemotherapy) [12][13][14]. It is difficult to estimate the incidence of second primary ma-

Purpose The objective of this study is to evaluate the benefits of radioactive iodine (RAI) treatment and the risk of second primary malignant (SPM) in RAI treated patients. Methods The cohort for this analysis consisted of individuals diagnosed with a first primary differentiated thyroid carcinoma (DTC), reported by SEER database in 1988–2016. Overall survival (OS) difference was estimated by Kaplan–Meier curves and Log-Rank test, and hazard ratios (HR) was obtained by cox proportional hazard model to evaluate the association between RAI and SPM. Standardized incidence ratios (SIR) were calculated to assess cancer incidence in relation to RAI and no-RAI groups and the general population. Results Among 130,902 patients, 61,210 received RAI and 69,692 did not and a total of 8,604 patients developed SPM. We found that OS was significantly higher in patients who received RAI than those who did not (P < 0.001). DTC survivors treated with RAI had increased risk of SPM in females (6.27% versus 5.97%, P = 0.043), particularly for SPM occurred in ovary (RAI group: 0.17%, no-RAI group: 0.12%, P = 0.039) and leukemia (RAI group: 0.22%, no-RAI group: 0.12%, P < 0.0001). In addition, RAI group in all age subgroups demonstrated higher SPM incidence than no-RAI group, and the incidence increased with age. Patients with primary thyroid cancer had a 16% elevated risk of developing SPM in all sites (SIR:1.16), 243% elevated risk in salivary glands (SIR:3.43), 119% elevated risk in kidneys (SIR:2.19), and 46% elevated risk in hematopoietic System (SIR:1.46). In general, the risk of developing SPM was higher in RAI group than in no-RAI group and general population. Conclusions Increased risks of SPM occur in female DTC survivors treated with RAI, which become more obvious with age increasing. Our research findings were beneficial to the formulation of radioactive iodine treatment strategies and the prevention of secondary tumors for patients with thyroid cancer of different genders and different ages.