• Journal of Radiation Protection and Research
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• v.19 no.1
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• pp.51-68
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• 1994

It is good method to use frequency of chromosome aberration in Lymphocytes for a biological dosimetry in cases of accidental exposure to radiation. But in cases of past exposure, biological dosimetry is limited because the frequency of aberration decreases by time after exposure. To provide a basic data for estimation of past radiation exposure, the changing pattern of frequency of unstable chromosome aberration by time interval after exposure was studied. Observation was made on peripheral lymphocytes of 41 blood samples from 20 patients treated for uterine cervical carcinoma and endometrial carcinoma. The patients received 50.4Gy radiation to whole pelvis. Elapsed times after the completion of radiation therapy were 1 day, 3, 6, 9, 12, 24, 52, 104, 156, 208, 260 and 520 weeks. All the blood sample were microcultured. The Ydr, Qdr and Qdra were calculated from frequency of unstable aberration. Ydr did not decrease for 3 weeks after radiation therapy, and thereafter, decreased very rapidly and reached 0.05 at two years after radiation therapy and decreased very slowly until 5 years after radiation therapy. Relationship between unstable chromosome aberration and time interval after radiation therapy was described as $Ydr=0.259{\times}exp(-0.0429T)+0.0560{\times}exp(-0.00106T)$ (time in weeks) Qdr remained constant at 1.51 until 24 weeks after radiation therapy and then decreased to 1.17 at 52 weeks. Therafter, it did not change. Qdra remained constant at 1.10 for 12 weeks after radiation therapy and decreased to 0.81 at 52 weeks. Thereafter, it remained constant. Two superimposed exponential Ydr disappearance rate suggests that it is possible to calculate the past exposure dose. When the elapsed time after exposure is short, Qdr and Qdra are useful papameters for biological dosimetry for past radiation exposure.