Objective: The aim of this study is to predict the risk of symptomatic sialadenitis after (131)I therapy using the early (third day post-therapy) and delayed (fifth or sixth day post-therapy) post-therapeutic (131)I scintigraphy images in patients with differentiated thyroid cancer (DTC).
Methods: Included in the study were 112 patients with DTC who underwent early and delayed (131)I scans after (131)I treatment. All patients had normal salivary gland function on salivary scintigraphy performed in the week before the (131)I 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.
Results: Of 112 patients, symptomatic sialadenitis was diagnosed in 46 patients (41 %). Of these 46 patients, 83 % (38 patients) had persistent (131)I uptake in the salivary glands on both early and delayed scans. Among 55 patients with persistent (131)I 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 (131)I 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 (131)I in bilateral parotid glands than other patients. Using visual analysis and SURs of right and left parotid glands on early (131)I 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 ± 6.3 h and 2.7 ± 0.8 Gy, and 22.1 ± 7.9 h and 2.8 ± 1.1 Gy, respectively.
Conclusions: Symptomatic sialadenitis can be predicted by post-therapeutic (131)I scintigraphy with high sensitivity. Post-therapeutic (131)I scintigraphy could provide effective information on the risk of symptomatic sialadenitis in DTC patients who underwent (131)I treatment.