title: A possible method using baseline hormonal levels to prescribe the appropriate oral therapeutic radioiodine dosage for Graves' disease.
abstract: OBJECTIVE
  The purpose of this study was to retrospectively examine the correlations of hormonal ratios with radioiodine I-131 therapeutic parameters and the potentiality of prescribing the therapeutic I-131 target dosage for an individual patient with Graves' disease using baseline serum levels of thyroid hormones.
  
  
  METHODS
  Serum T3, T4, and FT4 levels 6 and 12 months after I-131 therapy/baseline levels (hormonal ratios) were calculated for a total of 68 therapeutic courses in 57 patients with Graves' disease. The therapeutic parameters were absorbed dose (Gy), dose concentration (microCi/g) and oral dose (mCi). Linear regression analysis was performed for correlating hormonal ratios (X) and therapeutic parameters (Y).
  
  
  RESULTS
  Significant (P<0.05) negative correlations of the hormonal ratios were observed with absorbed dose (R -0.50 for T3, -0.61 for T4, and -0.46 for FT4 at 6 months, and -0.29 for T3, -0.44 for T4 at 12 months) and dose concentration (R -0.57 for T3, -0.58 for T4, and -0.49 for FT4 at 6 months and -0.27 for T3, -0.27 for T4 at 12 months), but not with oral dose at 6 months and 12 months or the absorbed dose and dose concentration for FT4 at 12 months. The correlations were higher at 6 months than at 12 months and in serum T4 than in serum T3 and FT4. The formulae for serum T4 at 6 months were as follows: Y (Gy)=109-53X and Y (microCi/g)=109-52X.
  
  
  CONCLUSIONS
  These results suggest that the hormonal ratios are significantly correlated with the absorbed dose and dose concentration. The formulae for serum T4 at 6 months may serve to prescribe the individual oral dosage for Graves' disease, although the correlation coefficients are about -0.6.
authors.affiliation: Department of Radiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, and Sagara Hospital, Kagoshima, 890-8544, Japan. nakajo@m.kufm.kagoshima-u.ac.jp
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nakajo
authors.forename: Shinsaku
authors.initials: S
authors.lastname: Tsuchimochi
authors.forename: Megumi
authors.initials: M
authors.lastname: Jinguji
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanabe
authors.forename: Tomoichi
authors.initials: T
authors.lastname: Umanodan
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Nakabeppu
mesh_terms: D000284:Administration, Oral; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004334:Drug Administration Schedule; D005260:Female; D006111:Graves Disease / Q000097:blood* / Q000175:diagnosis / Q000532:radiotherapy*; D006801:Humans; D007457:Iodine Radioisotopes / Q000008:administration & dosage*; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D019275:Radiopharmaceuticals / Q000008:administration & dosage; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D013963:Thyroid Hormones / Q000097:blood*; D016896:Treatment Outcome
chemical_list: D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013963:Thyroid Hormones