To compare empiric and calculated 131I activities using 2013 EANM recommendations. To look for predictive factors of therapeutic response to an empiric activity of 131I. To assess clinical situations favoring calculated treatment modalities.Patients and methods
Prospective monocentric study of clinical outcomes at 1 year follow-up in 86 patients with GD and MNG who received empiric 131I therapeutic activities (348–939 MBq). Differences between empiric and calculated activities were confronted to clinical outcomes. Physicians were not aware of the calculated activity at the time of prescription.Results
One year after treatment, 9% (5/57) of GD patients and 7% (2/29) of MNG patients were still in a hyperthyroid state. Thyroid volume was reduced by 67% for GD and by 50% for MNG. In GD, empiric 131I activities were higher than calculated ones (564±131 vs. 316±319 MBq, P<0.001) in 93% (53/57) of patients. Pretherapeutic thyroid volume (>26 ml for GD; >40 ml for MNG) was associated with persistent hyperthyroidism.Conclusion
Empirically administered 131I for GD and MNG was associated with very high efficacy in thyroid function control and no side effects. Thyroid volume reduction did not preclude treatment efficacy. Activity calculation could be a useful method for treating patients with GD and thyroid volumes higher than 26 ml or patients with MNG and thyroid volumes higher than 40 ml. A selective approach based on pretherapeutic thyroid volume and radioiodine biokinetics might improve treatment success.