Whole-body radioiodine effective half-life in patients with differentiated thyroid cancer

Abstract

Background: Radioactive131I (RAI) therapy is used in patients with differentiated thyroid cancer (DTC) after total thyroidectomy for remnant ablation, adjuvant treatment or treatment of persistent disease.131I retention data, which are used to indicate the time at which a131I 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 the131I whole-body retention in DTC patients during131I therapy. Methods: We monitored 166 DTC patients to follow the131I whole-body retention during131I therapy with a radioactivity detector fixed on the ceiling of each protected room. A linear regression fit permitted us to estimate the whole-body131I effective half-life in each patient, and a relationship was sought between patients’ clinical characteristics and whole-body effective131I half-life. Results: The effective131I half-life ranged from 4.08 to 56.4 h. At multivariable analysis, longer effective131I half-life was related to older age and extensive extra-thyroid disease. Conclusions:131I effective half-life during131I 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 of131I.