title: Comparison of effective I-131 half-life between thyroid hormone withdrawal and recombinant human thyroid-stimulating hormone for thyroid cancer: a retrospective study.
abstract: BACKGROUND
  Preparation for postoperative radioiodine ablation for differentiated thyroid carcinoma is performed by either thyroid hormone withdrawal or recombinant human thyroid-stimulating hormone (rhTSH) administration. There is little information on the impact of the method of preparation with respect to whole-body effective I-131 half-life and its potential clinical implications in the Australian setting.
  
  
  METHODS
  A retrospective study was performed on patients admitted for adjuvant radioiodine ablation for non-metastatic differentiated thyroid carcinoma at the Royal Adelaide Hospital over a 4½-year period from 2009. Dose rate measurements were analysed for 19 rhTSH and 31 thyroid hormone withdrawal patients.
  
  
  RESULTS
  The mean effective I-131 half-lives were 11.51 and 13.29 h for the rhTSH and thyroid hormone withdrawal groups, respectively, with no statistically significant difference between the two groups (P = 0.761). This result differs from previously published data where withdrawal periods were typically longer, resulting in slower renal clearance and longer half-lives for withdrawal patients.
  
  
  CONCLUSIONS
  Our study did not demonstrate a significant difference in whole-body effective half-life of I-131 between the two methods of preparation for radioiodine ablation. This suggests that putative advantages of rhTSH over withdrawal in terms of whole-body radiation dose, duration of hospital admission and quality of life may be sensitive to duration of withdrawal.
authors.affiliation: Department of Radiation Oncology, Royal Adelaide Hospital, Adelaide, South Australia, Australia.
authors.forename: Solveig
authors.initials: S
authors.lastname: Grenfell
authors.forename: Daniel
authors.initials: D
authors.lastname: Roos
authors.forename: James
authors.initials: J
authors.lastname: Rijken
authors.forename: Braden
authors.initials: B
authors.lastname: Higgs
authors.forename: Ian
authors.initials: I
authors.lastname: Kirkwood
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003131:Combined Modality Therapy / Q000379:methods; D005260:Female; D006207:Half-Life; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage* / Q000032:analysis*; D008297:Male; D008875:Middle Aged; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000032:analysis; D011879:Radiotherapy Dosage; D018714:Radiotherapy, Adjuvant / Q000379:methods; D011994:Recombinant Proteins / Q000008:administration & dosage; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000628:therapy*; D013972:Thyrotropin / Q000008:administration & dosage*; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; D013972:Thyrotropin
keywords: I-131 ablation; effective half-life; recombinant human thyroid-stimulating hormone; thyroid cancer; thyroid hormone withdrawal