Estimates of thyroid equivalent dose in Lithuania following the Chernobyl accident.

The volatile radioiodine was detected in Lithuania in the very first days after the Chernobyl accident. The proportion of gaseous 131I species of airborne iodine identified during that period exceeded from 2 to 4 times the aerosol fraction. The radioiodine activity of milk consumed by inhabitants of Lithuania varied over a broad range. 131I activity in milk reached a peak on the fourth day after deposition and then decreased with an effective half-time ranging from 4.2 +/- 0.6 d to 5.2 +/- 0.9 d. Thyroid examinations by dosimetric teams were not available in Lithuania for reasons beyond the control of experimenters. Because of this, thyroid equivalent doses were estimated using the modified ICRP three-compartment cyclic model. These calculations applied Monte Carlo methods and consideration of regional iodine deficiency to generate frequency distributions of equivalent doses to the infant and adult thyroid gland in three areas of Lithuania with different contamination levels.