title: Thyroid cancer: radiation safety precautions in 131I therapy based on actual biokinetic measurements.
abstract: OBJECTIVE
  To formulate radiation precautions for patients with thyroid cancer who are undergoing thyroid hormone withdrawal-induced hypothyroidism and iodine 131 ((131)I) therapy through actual biokinetic measurements.
  
  
  METHODS
  Informed consent and institutional review board approval were obtained. From October 2008 to December 2011, consecutive patients with differentiated thyroid cancer who had been prepared for (131)I ablation treatment or (131)I treatment for metastatic disease during follow-up were prospectively recruited. Calculations based on deduced whole-body retention and measured iodine biokinetics in thyroidal tissue were derived to determine the thyroidal and extrathyroidal compartment uptake fractions and effective half-lives. Precaution times necessary to avoid close contact with family members and the general public were derived from these parameters and regulatory dose limits.
  
  
  RESULTS
  Seventy-seven patients (36 with ablation treatments, 41 with follow-up treatments) were eligible for the analysis. Actual dose rates from patients after therapeutic (131)I administration were greatly lower than those described in the American Thyroid Association (ATA) and Nuclear Regulatory Commission (NRC) models: The mean initial dose rate at 0.3 m for patients with ablation treatment was only 28% (0.183/0.655 µSv/h/MBq) ± 2.9 (standard deviation) (range, 12.1%-38.3%) and 36% (0.183/0.511 µSv/h/MBq) ± 3.7 (range, 15.5%-49.1%) of that described in the NRC and ATA models, respectively; the equivalent values for patients with follow-up treatment were only 30% (0.195/0.655 µSv/h/MBq) ± 3.5 (range, 12.5%-45.3%) and 38% (0.195/0.511 µSv/h/MBq) ± 4.5 (range, 16.0%-58.1%), respectively. The actual mean effective (131)I half-life in the thyroid remnant tissue was greatly lower than that described in the ATA and NRC models: 47.6 versus 175.2 hours.
  
  
  CONCLUSIONS
  On the basis of the current dose limits, typically administered activities of 3.7 GBq to a patient with ablation treatment or 7.4 GBq to a patient with follow-up treatment required 3 days of sleeping apart for keeping the doses to pregnant women and children below 1 mSv. No precautions were required for non-cosleeping nonpregnant adult family members.
authors.affiliation: From the Department of Nuclear Medicine, West China Hospital, Sichuan University, 37 Guoxue Alley, Chengdu 610041, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Weiai
authors.initials: W
authors.lastname: Peng
authors.forename: Rui
authors.initials: R
authors.lastname: Huang
authors.forename: Rong
authors.initials: R
authors.lastname: Tian
authors.forename: Yu
authors.initials: Y
authors.lastname: Zeng
authors.forename: Anren
authors.initials: A
authors.lastname: Kuang
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006207:Half-Life; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics* / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011829:Radiation Dosage; D011835:Radiation Protection / Q000379:methods; D012307:Risk Factors; D013964:Thyroid Neoplasms / Q000532:radiotherapy*; D013965:Thyroidectomy; D014915:Whole-Body Counting
chemical_list: D007457:Iodine Radioisotopes