I-131 Activities as High as Safely Administrable (AHASA) for the Treatment of Children and Adolescents with Advanced Differentiated Thyroid Cancer

Aim: Differentiated thyroid carcinoma (DTC) in children and young adults is rare, can be aggressive, and often presents at advanced stages. In a population of young Belarusian patients with advanced DTC after the nuclear reactor accident at Chernobyl, we determined the activities that are as high as safely administrable (AHASA). Patients and Methods: In 180 children and adolescents, we studied 133 courses of I-131 thyroid remnant ablation (median age at ablation, 14.3 yr) and 250 courses of I-131 therapy (median age at therapy, 15.7 yr). Remnant ablation was performed with weight-adapted I-131 activities of a median of 51.8 MBq/kg (range, 23.9-73.8 MBq/kg); and residual disease therapy was performed with a median activity of 98.0 MBq/kg (range, 56.7-164.7 MBq/kg). The radiation absorbed dose to the blood (BD) per unit of activity administered for each treatment was deduced from whole-body retention data measured twice daily using ceiling probes. The AHASA activity was calculated assuming an upper limit of 2 Gy BD. Results: For I-131 ablation, the median weight-adjusted AHASA activity leading to a BD of 2 Gy was 407 MBq/kg (range, 137-661 MBq/kg). In three patients with extensive diffuse pulmonary metastases, the AHASA was lower than 200 MBq/kg. For patients receiving additional I-131 treatments after ablation, a median body weight-adapted AHASA activity of 406 MBq/kg (range, 210-775 MBq/kg) was calculated. Conclusion: Children and adolescents with advanced DTC can be treated with I-131 activities of at least 200 MBq/kg. For children with extensive pulmonary metastases, pretherapeutic dosimetry is needed to determine the AHASA. (J Clin Endocrinol Metab 96: E1268-E1271, 2011)