A possible method using baseline hormonal levels to prescribe the appropriate oral therapeutic radioiodine dosage for Graves' disease.
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.
Nakajo
Masayuki
M
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
Tsuchimochi
Shinsaku
S
Jinguji
Megumi
M
Tanabe
Hiroaki
H
Umanodan
Tomoichi
T
Nakabeppu
Yoshiaki
Y
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
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D013963:Thyroid Hormones