RT Journal Article SR Electronic T1 Iodine Biokinetics and Dosimetry in Radioiodine Therapy of Thyroid Cancer: Procedures and Results of a Prospective International Controlled Study of Ablation After rhTSH or Hormone Withdrawal JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP 648 OP 654 VO 47 IS 4 A1 Heribert Hänscheid A1 Michael Lassmann A1 Markus Luster A1 Stephen R. Thomas A1 Furio Pacini A1 Claudia Ceccarelli A1 Paul W. Ladenson A1 Richard L. Wahl A1 Martin Schlumberger A1 Marcel Ricard A1 Al Driedger A1 Richard T. Kloos A1 Steven I. Sherman A1 Bryan R. Haugen A1 Vincent Carriere A1 Carine Corone A1 Christoph Reiners YR 2006 UL http://jnm.snmjournals.org/content/47/4/648.abstract AB Technical aspects and results of the dosimetric assessments of postoperative radioiodine ablation in the framework of an international, prospective, controlled, randomized, comparative study of the effectiveness of ablation therapy with 3.7 GBq 131I in differentiated thyroid cancer after stimulation with recombinant human TSH (rhTSH) or by thyroid hormone withdrawal (THW) are presented. Methods: Sixty-three patients were randomized after thyroidectomy to either the THW or the rhTSH group. Scintigraphic neck images were acquired starting 48 h after radioiodine administration to assess biokinetics in the thyroid remnant. The activity in blood samples was quantified and data from whole-body probe measurements and scintigraphic whole-body scans were combined to deduce retention curves in blood and whole body, respectively. The absorbed dose to the blood was calculated using a modified approach based on the formalism of the MIRD Committee of the Society of Nuclear Medicine. Results: The effective half-time in the remnant thyroid tissue was significantly longer after rhTSH than THW (67.6 ± 48.8 vs. 48.0 ± 52.6 h, respectively; P = 0.01), whereas the observed differences of the mean 48-h 131I uptakes (0.5% ± 0.7% vs. 0.9% ± 1.0% after THW; P = 0.1) and residence times (0.9 ± 1.3 vs. 1.4 ± 1.5 h after THW; P = 0.1) between the rhTSH and THW groups were not statistically significant. The specific absorbed dose to the blood was significantly (P <0.0001) lower after administration of rhTSH (mean, 0.109 ± 0.028 mGy/MBq; maximum, 0.18 mGy/MBq) than after THW (mean, 0.167 ± 0.061 mGy/MBq; maximum, 0.35 mGy/MBq), indicating that higher activities of radioiodine might be safely administered after exogenous stimulation with rhTSH. Conclusion: Indication of an influence of the residence time of radioiodine in the blood on the fractional uptake into thyroid remnant was found. A novel regimen is proposed in which therapeutic activities to be administered are determined from the individual specific blood dose.