Impact of different approaches to calculation of treatment activities on achieved doses in radioiodine therapy of benign thyroid diseases

Abstract

PurposeRadioiodine has been used for the treatment of benign thyroid diseases for over 70 years. However, internationally, there is no common standard for pretherapeutic dosimetry to optimally define the individual therapy activity. Here, we analyze how absorbed tissue doses are influenced by different approaches to pretherapeutic activity calculation of varying complexity.MethodsPretherapeutic determination of treatment activity was retrospectively recalculated in 666 patients who had undergone radioiodine therapy for benign thyroid diseases (Graves’ disease, non-toxic goiter, and uni- and multinodular goiter). Approaches considering none, some, or all of a set of individual factors, including target volume, maximum radioiodine uptake, and effective half-life, were applied. Assuming individually stable radioiodine kinetics, which had been monitored twice a day under therapy, hypothetically achieved tissue doses based on hypothetically administered activities resulting from the different methods of activity calculation were compared to intended target doses.ResultsThe Marinelli formula yields the smallest deviations of hypothetically achieved doses from intended target doses. Approaches taking individual target volume into consideration perform better than fixed therapy activities, which lead to high variances in achieved doses and high deviations of hypothetically achieved doses from intended target doses.ConclusionElaborate pretherapeutic dose planning, taking individual radioiodine uptake, half-life, and target volume into consideration, should be used whenever possible. The use of disease-specific fixed activities cannot be recommended. Deviations of achieved tissue doses from target doses can already be significantly lowered by application of volume-adapted treatment activities if more elaborate means are not available.

Iratherapie dans la maladie de Basedow: place et efficacité

“…En effet, il existe 2 protocoles différents l´un utilisant des activités standards fixes indépendantes des caractéristiques du patient et l´autre utilisant des activités calculées en fonction de différents paramètres (taille de la thyroïde, pourcentage de la fixation du radiotraceur au niveau de la thyroïde). Les études faites comparant ces différentes approches thérapeutiques ont donné des résultats contradictoires [ 9 , 10 ]. Dans notre étude, nous avons opté pour l´activité standard.…”

The Role of Nuclear Medicine in the Clinical Management of Benign Thyroid Disorders. Part 2. Nodular Goiter, Hypothyroidism, and Subacute Thyroiditis

“…The initial estimate (i.e., 3.7 MBq 3 volume of functioning thyroid tissue as assessed by thyroid scintigraphy) is corrected by the 24-h radioiodine uptake value. More personalized dosimetry-based approaches to determine the activity of radioiodine for therapy (44) were discussed in part 1 of this continuing education article (1). Whereas in Graves' disease the target absorbed dose necessary to ablate hyperfunctioning thyroid tissue is between 200 and 400 Gy, data derived from external-beam radiation therapy for cancers of the head and neck suggest that an absorbed dose of between 100 and 150 Gy is sufficient for ablation of normal thyroid parenchyma (45,46).…”

A Clinical Debate: What Is the Therapeutic Choice for Recurrent Graves’ Hyperthyroidism?

“…Furthermore, both of these strategies can be applied using either low or high doses of radioiodine. Anyhow, it is shown that among fixed-dose strategies, radiation received by the thyroid is not related to the administered radioiodine dose (19,20). Comparing different treatment modalities like ATD and RIT in terms of efficacy and complications requires the implementation of standard treatment in each arm.…”