Effect of a diagnostic dose of 185 MBq 131I on postsurgical thyroid remnants.
Stunning of thyroid remnants after diagnostic scanning with 131I may limit 131I therapy. The follow-up scans and serum thyroglobulin levels of such patients have been studied.


METHODS
Three-hundred seventy-eight patients who underwent thyroidectomy for differentiated thyroid carcinoma were studied. Diagnostic scans were obtained with 185 MBq 131I; 7.2 wk afterward, the patients received 489 ablative treatments with 4 GBq 131I. A total of 1575 scans were obtained (pre- and posttreatment scans and 615 follow-up scans). The evolution of serum thyroglobulin levels was determined.


RESULTS
In all patients, the thyroid-stimulating hormone level was more than 30 microIU/mL. Posttherapy scans showed less uptake than did diagnostic scans or even showed negative findings in 99 patients (21%). In these patients, the mean time between diagnostic scanning and therapy was 7.9 wk. In 61 of these 99 patients (61.6%), follow-up scans have shown negative findings, serum thyroglobulin was less than 3 ng/mL, and antithyroglobulin antibodies were not present. Twenty-three patients (23.2%) have not undergone follow-up scanning yet. In 8 patients (8.1%), follow-up scans showed negative findings but serum thyroglobulin was more than 3 ng/mL. In 7 patients (7.1%), follow-up scans showed less uptake than posttherapy scans, but the findings were not yet negative and thyroglobulin was less than 3 ng/mL.


CONCLUSIONS
Our data suggest that a stunning effect does not exist for doses of 185 MBq 131I for diagnostic scans. However, a therapeutic effect may exist.
Bajén
M T
MT
Medicina Nuclear, Center de Tecnologia Diagnòstica, Tarrasa, Spain.
Mañé
S
S
Muñoz
A
A
García
J R
JR
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000032:analysis; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D011877:Radionuclide Imaging; D013954:Thyroglobulin / Q000097:blood / Q000276:immunology; D013961:Thyroid Gland / Q000000981:diagnostic imaging / Q000528:radiation effects*; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy* / Q000601:surgery; D013965:Thyroidectomy; D013972:Thyrotropin / Q000097:blood
D001323:Autoantibodies; D007457:Iodine Radioisotopes; D013972:Thyrotropin; D013954:Thyroglobulin