Thyroid Cancer Radiotheragnostics: the case for activity adjusted 131 I therapy.

Radiotheragnostics represents the systematic integration of diagnostic imaging and therapeutics using radionuclides targeting specific characteristics of tumor biology. Radioiodine (131 I) is the classic radiotheragnostic agent used for the diagnosis and treatment of differentiated thyroid cancer (DTC) based on sodium-iodine symporter expression in normal and neoplastic thyroid tissue. Application of radiotheragnostics principles in thyroid cancer involves using pre-ablation diagnostic scans (Dx Scans) for detection of iodine-avid regional and distant metastatic disease and patient-individualized targeted 131 I therapy with goal of maximizing the benefits of the first therapeutic 131 I administration. Clinically available nuclear medicine imaging technology has significantly evolved over the past 10 years with the introduction of hybrid SPECT/CT and PET/CT systems, as well as advances in iterative image reconstruction with modeling of image degrading physical factors. This progress makes possible the acquisition of accurate diagnostic radioiodine scintigraphy capable of identifying regional and distant metastatic disease, which can be used for 131 I treatment planning and delivery of activity adjusted 131 I therapy for achieving intended treatment goals (e.g. remnant ablation, adjuvant 131 I treatment and targeted 131-I treatment). The overarching aim of thyroid cancer radiotheragnostics is to optimize the balance between 131 I therapeutic efficacy and potential side-effects on non-target tissues.