Personalised medicine – Dosimetry in radioiodine therapy for benign thyroid disease

The EANM Guidelines for Dosimetry for Benign thyroid diseases [1] recommend two or more uptake measurements to estimate the residence time of I-131 in the thyroid, which when combined with the mass of the gland can be used to calculate the treatment activity. The guidelines also outline methods to estimate residence time using one early or one late uptake assessment, with subsequent loss of accuracy. The workup for therapy in our centre includes thyroid ultrasound and an I-131 uptake measurement. For patients with a solitary toxic nodule the uptake measurement combined with nodule size have been used to determine treatment activity. Patients with Grave’s disease and multinodular goitre were previously treated with fixed activities. Following a review of the treatment outcome for 130 patients we present a retrospective analysis which demonstrates that these fixed activities resulted in estimated thyroid doses which ranged over an order of magnitude. Subsequently we present our initial experiences of adopting the EANM Dosimetry guidelines using a minimum of two uptake measurements. For therapies such as I-131 therapy with high success rates (85%–90% in our centre), it has been difficult to justify the use of dosimetry in the past. However with the imminent implementation of the 97/43/EURATOM and to optimise the therapeutic benefit to the patient, it is essential that we begin to utilize available dosimetry techniques.