الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
Background Papillary thyroid cancer (PTC) represents most of cases of differentiated thyroid cancers. Thyroidectomy followed by radioactive iodine (RAI) remnant ablation represent the cornerstone management of many intermediate and high-risk patients according to American Thyroid Association (ATA). Objective This study evaluates the outcome of different used I131 ablation doses (80, 100 and 120 mCi) in intermediate and high-risk patients in our hospital and analyzes the predictors affecting RAI failure. Besides, survival analysis was conducted as a secondary objective of the study. Patients & Methods This is a retrospective study conducted over 63 patients diagnosed as PTC at our hospital from 2015 till 2020. Inclusion criteria included patient`s age 18-70 years at diagnosis, intermediate and high-risk patients according to ATA initial risk stratification system, 2015. Double malignancies, patients aged <18 years at diagnosis and low risk group were excluded. Successful ablation was defined as negative radiology using Whole body iodine scan (WBIS), either diagnostic or therapeutic, or neck US and undetectable serum thyroglobulin level (stimulated Tg<1 ng/ml, unstimulated Tg <0.2 ng/ml) in negative Tg anti-bodies setting. Failure of ablation defined as “ATA incomplete response; biological or structural failure and indeterminate repose”. Fisher’s exact test and 2 test were used for comparison between different groups. Results Among the 63 patients included in this study (17 males and 46 females), 41 were classified as intermediate risk, while 22 were classified as high risk based on the ATA guideline. Overall RAI ablation success, in both groups, was observed in 43/63 (68.25%) patients. Moreover, it was achieved in 31/41 (75.6%) intermediate risk patients and in 12/22 (54.5%) high risk patients. Pre-ablation stimulated Tg >1ng/ml was statistically significant negative predictor of ablation failure [P-value < 0.001, odd`s ratio 61.5, 95% CI (10.8-51.5)]. Conclusion There was no statistically significant difference between success rates of I131 doses in intermediate and high-risk groups. However, the failure rates were more after 120mCi due to the associated more aggressive underlying disease, especially higher risk patients so higher RAI activities are recommended for this risk group. Key Words: Papillary thyroid cancer, Radioactive iodine, Remnant ablation.