Accuracy of different means of dose calculation for radioiodine therapy in benign thyroid disease

Objectives: The use of radioiodine therapy is common in the treatment of benign thyroid disease. Several different strategies are used to a priori estimate the activity required for effective radioiodine therapy. To compare the accuracy of these concepts in achieving the intended dose, we calculated the individual effective dose which would have resulted by employing the different strategies in a group of 559 patients who were treated for benign thyroid disease.

Methods: Patients presenting consecutively between May 25, 2011 and 12^st September 12, 2012 were included in the study. Patients were treated for Graves’ disease (GD) (n=206), non-toxic goitre (NTG) (n=74) and toxic goitre (TG) (n=279). The following calculation estimation methods were used: M1: indication-based fixed activities, M2: standard activities per gram thyroid tissue, M3: standard activities corrected for measured volume and radioiodine uptake, calculated using standard radioiodine half-life, M4: calculation with the use of measured volume, radioiodine uptake and half-life as calculated by Marinelli’s formula. The accuracy of the different approaches was judged on the basis of the mean standard deviation from the intended dose.

Results: The intended dose would have been achieved by M1, M2, M3 and M4 with a mean standard deviation of +/ 133 Gy, 96 Gy, 107 Gy, and 58 Gy in GD. In NTG, the deviation would have been +/- 147 Gy (M1), 58 Gy (M2), 44 (M3), and 39 Gy (M4). In TG, deviation values from the intended dose of +/- 114 Gy (M1), 53 Gy (M2), 77 Gy (M3), and 71 (M4) would have been obtained.

Conclusion: Overall, a dosimetric approach with measured radioiodine uptake and half-life results in the best accuracy when aiming to achieve the intended dose. Interestingly, a simple correction of fixed activities for the target volume already results in a higher accuracy than the application of fixed activities. Research Support: