Abstract
BACKGROUND: The optimal dose of adjuvant radioiodine((131)I) therapy for differentiated thyroid cancer (DTC) remains controversial. This study aimed to determine the efficacy and prognostic impact of two doses of adjuvant (131)I therapy (3.7 GBq and 5.55 GBq) in DTC patients with unexplained TSH-stimulated Tg(sTg) elevation. METHODS: Data for eligible patients with DTC who received adjuvant (131)I therapy at our institution between January 2015 and December 2016 were retrospectively reviewed. The results of dynamic risk assessment of persistent and recurrent disease (PRD) and recurrence-free survival (RFS) were compared between the 3.7 GBq and 5.55 GBq (131)I groups using the chi-squared test, Fisher's exact test, log-rank test, and a Cox proportional hazards model. RESULTS: In total, 224 patients with DTC were enrolled. Six months after adjuvant (131)I therapy, 132 patients(58.9%) had an acceptable response and 92 (41.1%) had an unacceptable response. After a median follow-up duration of 6.7 years (range, 6.0-7.9), 12 patients (33.33%) had persistent disease and 24 (66.7%) had recurrent disease. One patient died during follow-up. The 5-year RFS rate after (131)I treatment was 91.7%. At 6 months after treatment, there was no significant between-group difference in efficacy or the incidence of PRD or RFS (P > 0.05). Univariate analysis revealed significant associations of (131)I whole-body scan combined with (131)I-WBS/SPECT results after (131)I treatment, and number of (131)I treatments with the incidence of PRD ( P = 0). In multivariate analysis, the number of surgeries (hazard ratio [HR] 3.147, 95% confidence interval [CI] 1.360-7.282, P = 0.007), number of (131)I treatments (HR 0.046, 95% CI 0.020-0.108, P = 0.001), and efficacy at 6 months after (131)I treatment (HR 0.287, 95% CI 0.113-0.732, P = 0.009) were significantly associated with RFS. CONCLUSIONS: The efficacy of adjuvant (131)I therapy and the prognosis in DTC patients with unexplained sTg elevation was unaffected by whether the dose is 3.7 GBq or 5.55 GBq. Prospective, large-scale, long-term and RCTs clinical studies are needed to confirm these findings.