(32) Dose-Related Response of Salivary Impairment in Radioactive Iodine Treatment for Thyroid Cancers

Abstract: Radioactive iodine (I131) is widely used in the treatment of thyroid malignancies; however, a common side effect is salivary gland dysfunction, particularly parotitis. This dysfunction can significantly impact patients’ quality of life. While it is known that salivary dysfunction following I131 treatment can be dose-dependent, the precise dose-response relationship remains unclear, with a lack of consensus regarding the thresholds and variability in patient responses.

This study conducted a mini-review of the literature to evaluate the dose-response relationship between I131 and salivary gland impairment. Inclusion criteria were: (1) Human studies; (2) Patients who received I131 treatment for thyroid malignancy; (3) Studies that reported outcomes related to I131 dosage and salivary gland response. Databases such as PubMed, Medline, and Embase were searched using MeSH terms “parotitis and I131” and “parotid and iodine and dose.” A total of 327 studies were initially retrieved, but only 5 studies met the inclusion criteria, and 4 level 4 case reports were excluded. A quality assessment scoring system was applied to evaluate the rigor of the included studies. These studies were analyzed for the reported doses of I131, the salivary glands affected, and the severity of dysfunction. Descriptive statistical analysis was employed to evaluate trends and correlations between I131 dosage and the severity of salivary gland impairment. Five studies involving a total of 664 patients met the criteria for inclusion.

The studies varied in duration, with follow-up periods ranging from short-term assessments to long-term monitoring. Descriptive statistics were used to summarize the dose-response relationships observed in the included studies. No advanced statistical tests were employed due to the lack of randomized controlled trials. Five studies met the inclusion criteria and reported on the salivary gland responses to I131 doses in thyroid cancer patients. Salivary dysfunction was primarily observed in the parotid glands, with the submandibular glands being relatively unaffected. A dose-dependent increase in the severity of gland dysfunction was noted, with higher doses correlating with more significant impairment. However, variations in patient responses were observed even at lower doses. No significant differences in gland dysfunction were noted in patients receiving doses below 150 mCi of I131. The studies suggested that while higher doses resulted in more severe symptoms of sialadenitis and xerostomia, some patients experienced gland dysfunction at doses lower than typically expected for these conditions.

The reviewed studies consistently indicated that higher doses of I131 are associated with greater impairment of salivary gland function, though no clear threshold was identified for when dysfunction would occur. Furthermore, the absence of randomized controlled trials in the literature limits the generalizability of these findings. The reviewed studies used various scoring systems, including salivary gland scintigraphy and visual assessment, to evaluate gland function, but these systems lacked standardization.

The dose-response relationship between I131 treatment and salivary gland dysfunction in thyroid cancer patients is complex and not fully understood. Although higher doses of I131 tend to cause more severe dysfunction, even lower doses can result in salivary gland impairment. The lack of uniform scoring systems and randomized controlled trials highlights the need for further prospective studies. Additionally, clinicians should remain vigilant in diagnosing and managing salivary gland dysfunction following I131 treatment to mitigate its impact on patients’ quality of life.
Table 1. Criteria for evaluation of the quality of studies with dose and salivary gland response.Table 2. Summary of studies on I-131 dose and salivary gland response.