Does underlying synchronous benign thyroid tissue have an effect on radioactive iodine ablation outcome in papillary thyroid cancer?

Document Type : Original Paper, Therapy

Authors

1 Nuclear Medicine Unit - Department of Clinical Oncology and Nuclear Medicine - Faculty of Medicine - Cairo University

2 Nuclear Medicine Unit - Department of Clinical Oncology and Nuclear Medicine, Faculty of Medicine, Cairo University

Abstract

Objective: to explore the effect of the histopathological nature of the remnant thyroid tissue on the success of the ablation after the first dose of RAI-131.
Methods: In this retrospective study, clinical and pathological data of patients with histopathologically proven low to intermediate risk PTC were reviewed. The RAI dose that was given to the patients ranged from 80 to 100 mCi. The clinical impact of the histopathology of the thyroid remnant was assessed by evaluating the ablation outcome at the post 6 months follow-up.
Results: Among a total of 130 patients, 33.8% had normal thyroid tissue remnant, 24.6% had Hashimoto’s thyroiditis, 23.1% had MNG and 18.5% had colloid nodular goiter. Diagnostic post 6-months scan was positive in 29.2% (n= 38) of cases indicating incomplete ablation and was negative in 70.8% (n= 92) indicating complete ablation. The difference between complete and incomplete ablation in relation to the thyroid tissue background was statistically significant (p-value <0.001). Hashimoto’s thyroiditis had a statistically significant different ablation outcome as compared to normal thyroid tissue, whereas the ablation outcome in the group of patients with MNG and colloid nodular goiter was not statistically different when compared to normal thyroid tissue. There was a statistically significant difference in the ablation outcome between patients with autoimmune pathology and patients with non-auto-immune pathology with a p-value of p<0.001. As regards the baseline tumor markers, there was a statistically significant lower mean value of baseline stimulated anti-TG in patients with compete ablation (mean was 60.73) compared to patients with incomplete ablation (mean was 132.81) with a p-value of p=0.018. Hashimoto’s thyroiditis was a significant independent predicting factor for RAI-131 ablation outcome on univariate and multivariate regression analyses with a p-value= 0.002.
Conclusion: Individualization of RAI-131 ablation dose should take into consideration the nature of the thyroid tissue remnant.

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