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Successful thyroid tissue ablation as defined by a negative whole-body scan or an undetectable thyroglobulin: a
Maroun Karam1, Paul J Feustel, Eric S Postal
1Division of Nuclear Medicine, Albany Medical College, Albany, NY 12208, USA. karamm@mail.amc.edu
Background:
Successful thyroid tissue ablation of patients with well-differentiated thyroid cancer can be defined by a negative whole-body scan (WBS) and/or an undetectable thyroglobulin (Tg). Variables associated with success are poorly understood. Tg measurement, although more sensitive than WBS, has not been firmly established as the sole monitoring method. In a previous study, we retrospectively evaluated the variables associated with scintigraphic success. Ablation dose (AD) was the only variable associated with success (odds ratio (OR): 1.96 per 1.85 GBq increment; 95% confidence interval (CI)=1.11-3.46).
Objectives:
(1) To determine if the variables associated with success are the same using Tg. (2) To determine whether Tg measurement can become the sole method for assessing ablation success.
Methods:
We performed the analysis using a Tg level <2 ng.ml-1 as a criterion for completed ablation. Data were available from 109 patients.
Results:
Univariate analysis showed an effect of stage (OR=0.05; 95% CI=0.01-0.23) and female sex (OR=2.8; 95% CI=1.14-6.89). Multivariate analysis demonstrated only stage to be a significant predictor of success. Ablation was successful by both methods in 62/109 patients and it failed by both in 10/109. There were 21 WBS- Tg+ and 16 WBS+ Tg- patients.
Conclusions:
Investigation of the variables associated with successful ablation yields different results depending on the definition of success. There was a significant incidence of WBS+ Tg- cases after initial ablation. Until it is firmly established that such patients have a benign course both monitoring methods should be used.