Molecular radiotheragnostics in thyroid disease

Abstract

Molecular radiotheragnostics directly links nuclear medicine diagnostic imaging to therapy. The imaging study is used to detect a specific molecular target associated with a disease process. A radiotherapeutic molecule with a similar biodistribution to the diagnostic agent can then be used to deliver targeted therapy.Molecular radiotheragnostics have been applied to manage both benign and malignant thyroid disease since the 1940s. The specific molecular pathway targeted is the sodium/iodide symporter (NIS) located on the basolateral membrane of the thyroid follicular cell. Radiolabelling of iodide or a similar ion allows targeting of the NIS system with radiopharmaceuticals for imaging (¹²³I-radioiodine and ^99mTc-pertechnetate) and treatment (¹³¹I-radioiodine) by virtue of their gamma ray and beta-particle emissions, respectively.Scintigraphic imaging directly guides ¹³¹I-radioiodine treatment planning to maximise therapeutic benefit while minimising adverse reactions, in a personalised medicine approach.

Keywords: 99mTc-pertechnetate; DTC (differentiated thyroid cancer); NIS (sodium/iodide symporter); molecular; radioiodine; radiotheragnostic; thyroid; thyrotoxicosis.

Fig 1.

Scintigraphic imaging reflecting physiological and pathophysiological NIS-mediated iodide uptake in Graves’ disease (A) and a toxic nodule (B).

Fig 2.

Inverse relationship ­between iodine and FDG avidity – a reflection of ­tumour differentiation. A – ¹³¹I-radioiodine anterior neck image shows no iodine avid disease within the neck (salivary gland and nasal uptake is physiological); B – ¹⁸F-FDG PET-CT coronal fused image shows bilateral FDG-avid neck disease. CT = computerised tomography; FDG = fluorodeoxyglucose; PET = positron emission tomography