title: Timing of Hormone Withdrawal in Children Undergoing 131I Whole-Body Scans for Thyroid Cancer.
abstract: BACKGROUND
  Little objective pediatric data exist to guide the optimal time needed to achieve thyroid-stimulating hormone (TSH) levels ≥30 μIU/mL prior to performing 131I or 123I whole-body scan (WBS) imaging in children with thyroid cancer in the post-thyroidectomy period or after hormone discontinuation.
  
  
  METHODS
  Retrospective study of patients aged 5-19 years who underwent WBS. Patient data collection included type and duration of withdrawal (liothyronine [L-T3], levothyroxine [L-T4], or post-thyroidectomy status without hormonal replacement) and TSH measured prior to WBS (level and timing).
  
  
  RESULTS
  A total of 175 TSH level measurements were performed in 68 patients. Thirty-five TSH values were obtained 2-7 weeks postoperatively and 101 values were obtained 2-8 weeks post L-T4 withdrawal. One patient in each group had a TSH level <30 μIU/mL. There was no difference in TSH levels between 3 weeks and 4 weeks postoperatively (p = 0.14) or post L-T4 cessation (p = 0.21). Thirty-nine TSH measurements were obtained 1-28 days post L-T3 withdrawal. Three patients had to be rescheduled due to inadequate TSH levels, including one after 14 days L-T3 withdrawal.
  
  
  CONCLUSIONS
  TSH levels ≥30 μIU/mL were achieved at 3 weeks post thyroidectomy or after L-T4 withdrawal and after at least 2 weeks following L-T3 cessation.
authors.affiliation: Department of Medical Imaging, Nuclear Medicine Service, CHU Sainte-Justine, Montréal, QC, Canada.
authors.forename: Sophie
authors.initials: S
authors.lastname: Turpin
authors.forename: Raymond
authors.initials: R
authors.lastname: Lambert
authors.forename: Cheri
authors.initials: C
authors.lastname: Deal
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D019275:Radiopharmaceuticals / Q000008:administration & dosage*; D012189:Retrospective Studies; D013964:Thyroid Neoplasms / Q000097:blood / Q000000981:diagnostic imaging / Q000188:drug therapy; D013972:Thyrotropin / Q000008:administration & dosage*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D051598:Whole Body Imaging
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D014284:Triiodothyronine; D013972:Thyrotropin; D013974:Thyroxine