LAUSR

Objective To predict the successful outcome of radioactive iodine-131 (I-131) ablation treatment for differentiated thyroid cancer (DTC) patients using quantitative parameters from therapeutic I-131 SPECT/CT. Methods This retrospective study enrolled 145 DTC patients (41 males and 104 females) who had radioactive iodine-131 (I-131) (RAI) ablation therapy following thyroidectomy surgery from July 2020 to May 2021. The median age was 47 years (24-65 years). All the patients underwent therapeutic I-131 thyroid SPECT/CT scan after RAI ablation. The I-131 uptake quantitative parameters SUVmax, SUVmean %ID and ∆Tg (defined as the Tg level before RAI ablation minus the Tg level after six months) were assessem. Successful ablation treatment was defined as the level of TSH-stimulated Tg≤1 ng/mL and the disappearance of the thyroid bed on a whole-body I-131 scan six months or later after ablation treatment. Results The quantitative parameters from therapeutic I-131 SPECT/CT of the successful ablation (n=130) group with SUVmax 7.74 (3.84, 18.78) g/ml, SUVmean 4.02 (2.11, 6.39) g/ml and %ID 2.21% (0.67%, 7.30%) were significantly higher than those of the unsuccessful (n=15) group 0.75 (0.53, 1.28) g/ml, 0.44 (0.29, 0.79) g/ml and 0.16% (0.06%, 1.48%) (Z=-5.87, -5.71 and -4.99, all P < 0.001). SUVmax, SUVmean and %ID were positively correlated with ΔTg (all P < 0.001). Receiver operating characteristics curve analysis showed that %ID performed better predict value than either SUVmax (AUC=0.914, and 0.874, P=0.009) or SUVmean (AUC= 0.863 P=0.002). SUVmax, SUVmean and%ID (OR =1.50, 2.85 and 1.01 all P < 0.001) were all independent predictors of successful RAI ablation. Conclusion The quantitative parameters of therapeutic I-131 SPECT/CT were related to the efficacy of ablation treatment, and %ID could predict the successful outcome of ablation treatment for DTC patients.