Whole-Body Radioiodine Effective Half-Life in Patients with Differentiated Thyroid Cancer

Background: Radioactive (131)I (RAI) therapy is used in patients with differentiated thyroid cancer (DTC) after total thyroidectomy for remnant ablation, adjuvant treatment or treatment of persistent disease. (131)I retention data, which are used to indicate the time at which a (131)I treated DTC patient can be released from the hospital, may bring some insights regarding clinical factors that prolong the length of hospitalization. The aim of this study was to investigate the (131)I whole-body retention in DTC patients during (131)I therapy. Methods: We monitored 166 DTC patients to follow the (131)I whole-body retention during (131)I therapy with a radioactivity detector fixed on the ceiling of each protected room. A linear regression fit permitted us to estimate the whole-body (131)I effective half-life in each patient, and a relationship was sought between patients’ clinical characteristics and whole-body effective (131)I half-life. Results: The effective (131)I half-life ranged from 4.08 to 56.4 h. At multivariable analysis, longer effective (131)I half-life was related to older age and extensive extra-thyroid disease. Conclusions: (131)I effective half-life during (131)I treatment in DTC patients is highly variable among patients and is significantly longer in older and in patients with RAI uptake in large thyroid remnants or in extrathyroidal disease that significantly prolongs the whole-body retention of (131)I.