Comparison of different thyroid committed doses in radioiodine therapy for Graves' hyperthyroidism.
Despite vast worldwide experience in the use of 131I for treating Graves' disease (GD), no consensus of opinion exists concerning the optimal method of dose calculation. In one of the most popular equations, the administered (131)I dose is directly proportional to the estimated thyroid gland volume and inversely proportional to the measured 24-hour radioiodine uptake. In this study, we compared the efficiency of different tissue-absorbed doses to induce euthyroidism or hypothyroidism within 1 year after radioiodine therapy in GD patients. The study was carried out in 134 GD patients (age, 53 +/- 14 year; range, 16-82 year; thyroid volume, 28 +/- 18 mL; range, 6-95 mL; average 24-hour thyroid uptake, 72%) treated with (131)I therapy. The average radioiodine activity administered to patients was 518 +/- 226 MBq (range, 111-1110). The corresponding average thyroid absorbed dose, calculated by a modified Medical Internal Radiation Dose (MIRD) equation was 376 +/- 258 Gy (range, 99-1683). One year after treatment, 58 patients (43%) were hypothyroid, 57 patients (43%) were euthyroid, and 19 patients (14%) remained hyperthyroid. The patients were divided into 3 groups: 150 Gy (n = 32), 300 Gy (n = 58) and >300 Gy (n = 44). No significant difference in the rate of recurrent hyperthyroidism was found among the 3 groups (150 Gy: 15%; 300 Gy: 14%; and > or =300 Gy: 14%; chi-square test, p = 0.72). Whereas, the rate of hypothyroidism in the 3 groups was significantly correlated with the dose (150 Gy: 30%; 300 Gy: 46%; >300 Gy: 71%; chi-square test, p = 0.0003). The results obtained in this study show no correlation between dose and outcome of radioiodine therapy (in terms of persistent hyperthyroidism) for thyroid absorbed doses > or =150 Gy, while confirming the relation between the thyroid absorbed dose and the incidence of hypothyroidism in GD patients.
Grosso
Mariano
M
Regional Center of Nuclear Medicine, University of Pisa Medical School, I-56126 Pisa, Italy. m.grosso@med.unipi.it
Traino
Antonio
A
Boni
Giuseppe
G
Banti
Elena
E
Della Porta
Mauro
M
Manca
Gianpiero
G
Volterrani
Duccio
D
Chiacchio
Serena
S
AlSharif
Abedallatif
A
Borsò
Elisa
E
Raschillà
Rosanna
R
Di Martino
Fabio
F
Mariani
Giuliano
G
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006111:Graves Disease / Q000532:radiotherapy*; D006801:Humans; D006980:Hyperthyroidism / Q000532:radiotherapy*; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D011874:Radiometry / Q000379:methods; D013961:Thyroid Gland / Q000378:metabolism / Q000473:pathology / Q000528:radiation effects*; D013997:Time Factors; D016896:Treatment Outcome
D007457:Iodine Radioisotopes