Sequential biological dosimetry after a single treatment with iodine-131 for differentiated thyroid carcinoma.
To determine the cytogenetic and genotoxic risk associated with therapeutic exposure to 131I (3.7 GBq) in 50 patients with differentiated thyroid carcinoma, we estimated the dosimetric index that reflects the dose to the circulating lymphocytes on Day 4 and at several time intervals after exposure over a period of 2 yr.


METHODS
Chromosomal aberrations were scored in peripheral lymphocytes obtained before and then 4 days, 3 mo, 6 mo, 1 yr and 2 yr after the first administration of 3.7 GBq 131I according to two methods: conventional cytogenetics and chromosome 4 painting.


RESULTS
The dosimetric index was 0.52 Gy on Day 4, 0.49 Gy at 3 mo, 0.45 Gy at 6 mo, 0.44 Gy at 1 yr and 0.42 Gy at 2 yr by conventional cytogenetics and 0.47 Gy on Day 4, 0.45 Gy at 3 mo, 0.44 Gy at 6 mo, 0.43 Gy at 1 yr and 0.42 Gy at 2 yr by chromosome 4 painting. We found a decrease in the frequency of chromosomal aberrations between Day 4 and 3 mo after exposure. This may be due to the decrease of lymphocyte counts shortly after 131I administration, which will recover later on. In contrast, the number of anomalies remained constant starting 3 mo after 131I administration.


CONCLUSIONS
These techniques permit retrospective biological dosimetry for up to 2 yr after therapeutic exposure to 131I.
M'Kacher
R
R
Radioprotection Laboratory-Nuclear Medicine, Institut Gustave Roussy, Villejuif, France.
Légal
J D
JD
Schlumberger
M
M
Aubert
B
B
Beron-Gaillard
N
N
Gaussen
A
A
Parmentier
C
C
D000328:Adult; D000368:Aged; D002869:Chromosome Aberrations; D002894:Chromosomes, Human, Pair 4; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007457:Iodine Radioisotopes / Q000493:pharmacokinetics / Q000627:therapeutic use*; D018655:Lymphocyte Count; D008297:Male; D008875:Middle Aged; D011879:Radiotherapy Dosage; D013964:Thyroid Neoplasms / Q000532:radiotherapy*
D007457:Iodine Radioisotopes