Prediction of risk for symptomatic sialadenitis by post-therapeutic dual I-131 scintigraphy in patients with differentiated thyroid cancer

Abstract

The aim of this study is to predict the risk of symptomatic sialadenitis after I-131 therapy using the early (third day post-therapy) and delayed (fifth or sixth day post-therapy) post-therapeutic I-131 scintigraphy images in patients with differentiated thyroid cancer (DTC). Included in the study were 112 patients with DTC who underwent early and delayed I-131 scans after I-131 treatment. All patients had normal salivary gland function on salivary scintigraphy performed in the week before the I-131 treatment. Scintigraphy images were visually analyzed and the salivary gland-to-background uptake ratio (SUR) and percent change of the SUR between early and delayed scans were calculated. Calculation of effective half-life and absorbed dose in the salivary glands was performed based on the MIRD schema. Of 112 patients, symptomatic sialadenitis was diagnosed in 46 patients (41 %). Of these 46 patients, 83 % (38 patients) had persistent I-131 uptake in the salivary glands on both early and delayed scans. Among 55 patients with persistent I-131 uptake in the salivary glands, 69 % experienced symptomatic sialadenitis, while only 14 % of the other 57 patients experienced symptomatic sialadenitis (p < 0.0001). On the early I-131 scintigraphy, SURs of bilateral parotid glands on early scan in patients with symptomatic sialadenitis were significantly higher than in other patients (p = 0.001 for right and p = 0.004 for left). Further, patients with symptomatic sialadenitis had a higher decreasing rate of the SUR and shorter effective half-life of I-131 in bilateral parotid glands than other patients. Using visual analysis and SURs of right and left parotid glands on early I-131 scan as parameters, the sensitivities for predicting symptomatic sialadenitis were 83, 80, and 93 %, respectively. The mean values of effective half-life and absorbed dose in the parotid and submandibular glands were 20.8 +/- A 6.3 h and 2.7 +/- A 0.8 Gy, and 22.1 +/- A 7.9 h and 2.8 +/- A 1.1 Gy, respectively. Symptomatic sialadenitis can be predicted by post-therapeutic I-131 scintigraphy with high sensitivity. Post-therapeutic I-131 scintigraphy could provide effective information on the risk of symptomatic sialadenitis in DTC patients who underwent I-131 treatment.