A comparative study of initial 131I therapy and reoperation for detection and treatment of residual lymph node metastasis in patients with papillary thyroid cancer

Purpose This study assesses the diagnostic performance of 131I SPECT/CT and treatment efficacy of initial postoperative radioiodine (RAI) compared with reoperation on residual lymph node metastasis (LNM). Methods Patients with iodine-avid LNM detected on postoperative 131I SPECT/CT and who underwent re-operative dissection within 12 months were included. LNMs (numbers and locations) detected via both methods were compared. The ongoing risk stratification was used to evaluate the therapeutic response to RAI and reoperation. Results Fifty-three patients with 95 iodine-avid LNMs detected by 131I SPECT/CT were enrolled in this study. A total of 51 (96.2%) patients had 212 LNMs confirmed by reoperation (p=0.004). The sensitivity and specificity of 131I SPECT/CT in detecting LNM were 44.8% (95/212) and 91.6% (87/95), respectively. The location frequency of residual LNMs found by 131I SPECT/CT was similar to that of reoperation (p=0.057). Excluding 2 false-positive patients, the remaining 51 patients were in structural incomplete response (SIR) after a single RAI treatment. Sixteen patients were evaluated on a second RAI treatment after reoperation. The SIR, biochemical incomplete response (BIR), indeterminate response (IR) and excellent response (ER) were 4 (23.5%), 4 (23.5%),5 (29.4%) and 3 (17.6%), respectively (p=0.000). Conclusion 131I SPECT/CT has high specificity but relatively low sensitivity in finding all residual LNMs. Reoperation is more effective than RAI therapy, however, less than 20% of patients achieved ER. The success rate must be balanced with the risk of reoperation for residual LNMs.