Predictive value of dual-phase ¹³¹I WBS in salivary gland dysfunction in patients with DTC treated with ¹³¹I after surgery

Objective To investigate the relationship between the ¹³¹I decay metabolic rate (DMR) of salivary gland and salivary gland dysfunction, and to evaluate the predictive value of dual-phase ¹³¹I whole body scan (WBS) in salivary gland dysfunction in patients with differentiated thyroid carcinoma (DTC) treated with ¹³¹I after surgery.

Methods A retrospective analysis was conducted on 60 postoperative patients with DTC (including 19 males and 41 females, aged 45.6±12.6 years) and without salivary gland symptoms who received their first ¹³¹I treatment at Baoding NO.1 Central Hospital from May 2020 to May 2023. All patients underwent salivary gland scintigraphy (SGS) before treatment and completed the multidisciplinary salivary gland society Q3 (MSGS-Q3) survey questionnaire. The patients discontinued levothyroxine sodium tablets for 3 weeks and adhered to a low-iodine diet. When thyroid-stimulating hormone levels exceeded 30 mU/L, the patients received ¹³¹I ablation treatment (hereinafter referred to as the first treatment). ¹³¹I WBS was performed within the same time interval on the second and fourth days of treatment. All patients underwent ¹³¹I treatment for recurrent and metastatic lesions or adjuvant treatment (hereinafter referred to as the second treatment) after 3–6 months. Two months after the first treatment, the MSGS-Q3 was completed. The patients were divided into symptomatic and asymptomatic groups based on the presence of salivary gland symptoms (a MSGS-Q3 score >5.00 was considered indicative of salivary gland symptoms). The ¹³¹I DMR of salivary gland was calculated by delineating regions of interest on two consecutive ¹³¹I WBS images and recording the radiation counts for bilateral salivary glands. Two months after the second treatment, the MSGS-Q3 was completed again, and the patients in the first asymptomatic group were further divided into symptomatic and asymptomatic groups based on the presence of salivary gland symptoms. Inter-group comparison of ¹³¹I DMR of salivary gland was performed using the Mann-Whitney U rank sum test. The sensitivity and specificity of ¹³¹I DMR of parotid and submandibular glands after the first treatment were assessed through receiver operating characteristic (ROC) curve analysis for predicting salivary gland dysfunction in DTC patients treated with ¹³¹I after surgery, and the areas under the curve (AUC) were calculated. The correlation between the ¹³¹I DMR of parotid and submandibular glands after the first treatment and MSGS-Q3 score after the first treatment was assessed through Spearman correlation analysis.

Results SGS confirmed normal salivary gland uptake and excretion functions before treatment. The MSGS-Q3 score before treatment was 0 (0, 0.75) points, and all scores were ≤5.00 points. Differences in the ¹³¹I DMR of parotid glands (84.0%±9.8% vs. 91.2%(86.2%, 94.8%), Z=−2.113, P=0.034) and submandibular glands (77.5%±10.7% vs. 87.7%(83.1%, 91.0%), Z=−3.049, P=0.002) were statistically significant between the symptomatic (n=18) and asymptomatic groups (n=42) in the first treatment. The ROC AUC of the ¹³¹I DMR of parotid and submandibular glands after the first treatment were 0.673(95%CI: 0.523–0.823) and 0.750(95%CI: 0.601–0.899), respectively. When the optimal cutoff values of the ¹³¹I DMR of parotid and submandibular glands were 84.9% and 77.9%, respectively, sensitivity and specificity for predicting salivary gland dysfunction in patients with DTC treated with ¹³¹I after surgery were respectively 81.0% and 44.4% (parotid gland) and 83.3% and 61.1% (submandibular gland). However, no statistically significant differences (Z=0.984, 0.249; both P>0.05) in the ¹³¹I DMR of parotid and submandibular glands after the first treatment were observed between the symptomatic (n=14) and asymptomatic groups (n=28) after the second treatment. After the first treatment, the ¹³¹I DMR of parotid gland (R₁=−0.358, P₁=0.013), and the ¹³¹I DMR of submandibular gland (R₂=−0.650, P₂<0.001) were negatively correlated with MSGS-Q3 score after the first treatment.

Conclusions The ¹³¹I DMR calculated by the dual-phase ¹³¹I WBS serves as a useful predictor of salivary gland dysfunction in patients with DTC treated with ¹³¹I after surgery. However, ¹³¹I DMR values from the first treatment has no clinical significance for predicting salivary gland dysfunction in patients after the second treatment.