Thyroidal uptake and radiation dose after repetitive I-131-MIBG treatments: influence of potassium iodide for thyroid blocking.
BACKGROUND
In I-131-MIBG therapy, I-131-iodide can be released from the I-131-MIBG molecule. Hypothyroidism might result from the undesirable irradiation of the thyroid gland. To prevent this, stable iodide such as potassium iodide (KI) is given to oversaturate the thyroid before I-131-MIBG is administered.


METHODS
In the present study, the incidence of hypothyroidism (elevated TSH) was correlated with the thyroidal uptake of I-131 and dose (MIRD dosimetry) after 35 individual treatments in ten patients. Iodine-131-MIBG therapy was performed using a modified dosage of 1.9-11.1 GBq (50-300 mCi) IV. Premedication with KI was done as recommended with a dose of 100 mg KI orally from 2 days before until 4 weeks after I-131-MIBG.


RESULTS
The absorbed thyroidal dose amounted to a very variable range of 0.2 (patient # 1) up to 30.0 (patient 3) Gy with 7.1 +/- 7.9 Gy per treatment and 24.1+/- 19.2 Gy per patient (mean+/- SD), despite the same and compliantly taken KI premedication protocol. Up to now, 4/10 or 40% of patients have developed hypothyroidism after a mean follow-up period of 11 months and a mean total administered dose of 18.7 GBq (505 mCi). A trend towards higher thyroidal doses was seen in the hypothyroid patients.


CONCLUSIONS
This study observes a general high inter- and intra-individual variability in radio-iodide uptake in the thyroid after I-131-MIBG therapy despite KI premedication, as well as possible occurrence of hypothyroidism. A dose-response relationship needs confirmation on a larger cohort of patients to reach statistical value. An alternative thyroid cytoprotection strategy for possible long-term survivors may be considered.
Brans
Boudewija
B
Division of Nuclear Medicine, Ghent University Hospital, Belgium. boudewijn.brans@rug.ac.be
Monsieurs
Myriam
M
Laureys
Genevieve
G
Kaufman
Jean-Marie
JM
Thierens
Hubert
H
Dierckx
Rudi A
RA
D019797:3-Iodobenzylguanidine / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D000328:Adult; D000368:Aged; D000970:Antineoplastic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D002648:Child; D002675:Child, Preschool; D004307:Dose-Response Relationship, Radiation; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000139:chemically induced; D007457:Iodine Radioisotopes / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics* / Q000652:urine; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000517:prevention & control; D018358:Neuroendocrine Tumors / Q000532:radiotherapy*; D011193:Potassium Iodide / Q000008:administration & dosage / Q000494:pharmacology*; D011292:Premedication; D019275:Radiopharmaceuticals / Q000008:administration & dosage / Q000009:adverse effects / Q000493:pharmacokinetics*; D013961:Thyroid Gland / Q000187:drug effects / Q000378:metabolism*; D013964:Thyroid Neoplasms / Q000517:prevention & control; D013972:Thyrotropin / Q000097:blood
D000970:Antineoplastic Agents; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D011193:Potassium Iodide; D019797:3-Iodobenzylguanidine; D013972:Thyrotropin