title: The absorbed dose to the blood is a better predictor of ablation success than the administered 131I activity in thyroid cancer patients.
abstract: OBJECTIVE
  The residence time of (131)I in the blood is likely to be a measure of the amount of (131)I that is available for uptake by thyroid remnant tissue and thus the radiation absorbed dose to the target tissue in (131)I ablation of patients with differentiated thyroid cancer (DTC). This hypothesis was tested in an investigation on the dependence of the success rate of radioiodine remnant ablation on the radiation absorbed dose to the blood (BD) as a surrogate for the amount of (131)I available for iodine-avid tissue uptake.
  
  
  METHODS
  This retrospective study included 449 DTC patients who received post-operative (131)I ablation in our centre in the period from 1993 to 2007 and who returned to us for diagnostic whole-body scintigraphy. The BD was calculated based on external dose rate measurements using gamma probes positioned in the ceiling. Success of ablation was defined as a negative diagnostic (131)I whole-body scan and undetectable thyroglobulin levels at 6 months follow-up.
  
  
  RESULTS
  Ablation was successful in 56.6% of the patients. The rate of successful ablation correlated significantly with BD but not with the administered activity. Patients with blood doses exceeding 350 mGy (n = 144) had a significantly higher probability for successful ablation (63.9%) than the others (n = 305, ablation rate 53.1%, p = 0.03). In contrast, no significant dependence of the ablation rate on the administered activity was observed.
  
  
  CONCLUSIONS
  The BD is a more powerful predictor of ablation success than the administered activity.
authors.affiliation: Department of Nuclear Medicine, University of Würzburg, Oberdürrbacher Straße 6, 97080, Würzburg, Germany. verburg_e@klinik.uni-wuerzburg.de
authors.forename: Frederik A
authors.initials: FA
authors.lastname: Verburg
authors.forename: Michael
authors.initials: M
authors.lastname: Lassmann
authors.forename: Uwe
authors.initials: U
authors.lastname: Mäder
authors.forename: Markus
authors.initials: M
authors.lastname: Luster
authors.forename: Christoph
authors.initials: C
authors.lastname: Reiners
authors.forename: Heribert
authors.initials: H
authors.lastname: Hänscheid
mesh_terms: D055011:Ablation Techniques; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000097:blood / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000097:blood* / Q000601:surgery* / Q000628:therapy; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes