Abstract
Background: Radioactive 131I (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 a 131I 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 131I whole-body retention in DTC patients during 131I therapy. Methods: We monitored 166 DTC patients to follow the 131I whole-body retention during 131I therapy with a radioactivity detector fixed on the ceiling of each protected room. A linear regression fit permitted us to estimate the whole-body 131I effective half-life in each patient, and a relationship was sought between patients’ clinical characteristics and whole-body effective 131I half-life. Results: The effective 131I half-life ranged from 4.08 to 56.4 h. At multivariable analysis, longer effective 131I half-life was related to older age and extensive extra-thyroid disease. Conclusions: 131I effective half-life during 131I 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 131I.
Highlights
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 known persistent disease
The efficacy of Radioactive I (RAI) therapy has been related to the radiation dose delivered to normal and neoplastic thyroid tissues [1,2,3]
Treatment conditions should optimize the radiation dose delivered to thyroid tissues and minimize the radiation dose delivered to extrathyroidal tissues
Summary
The efficacy of RAI therapy has been related to the radiation dose delivered to normal and neoplastic thyroid tissues [1,2,3]. The delivery of significant radiation doses to extrathyroidal tissues may induce side effects [4,5,6,7]. Treatment conditions should optimize the radiation dose delivered to thyroid tissues and minimize the radiation dose delivered to extrathyroidal tissues. The radiation doses delivered to normal and neoplastic thyroid tissue can be estimated by lesion dosimetry from the initial uptake and effective 131 I half-life in the thyroid tissue [9,10,11,12]. To estimate doses absorbed by extrathyroidal tissues, the Medical Internal Radiation Dose formalism is generally adopted [13]. Data published in report 53 of the International Commission on Radiological
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