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KMID : 0876319990010010051
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Cachon Medical Journal
1999 Volume.1 No. 1 p.51 ~ p.60
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The Dose-dependent Frequency of Chromosomal Aberrations in Blood Cells of Radioiodine-Treated Thyroid Cancer Patients
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Kim Jong-Ho
Kim Chong-Soon
Kim Eun-Sil
Kim Myung-Seon
Koo Chun-Hee
Lee Jae-Yong
Song Myung-Jae
Chung June-Key
Lee Myung-Chul
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Abstract
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We evaluated the dose-response relationship between radioiodine absorbed dose to blood(D) and the frequency of unstable chromosomal aberrations using Ydr(dicentric or ring chromosomes) which is the number of cultured peripheral venous lymphocyte of dicentric or ring chromosomes among such lymphocytes in blood cells of radioiodine-treated thyroid cancer patients. After thyroidectomy, three groups of patients(total, 27) with differentiated thyroid cancer were treated with 131I, as follows: 3.7GBq to remnant thyroid(n=10), 5.55GBq to regional lymph nodes(n=15) and 7.4GBq to distant metastasis(n=6). Hematological, biological and indirect physical dosimetry were performed for the patients and biological dosimetry of in vitro irradiation with 131I at doses ranging from 0.05GBq to 6.00Gy was performed in peripheral venous blood of normal healthy subjects. Frequency of unstable chromosomal aberrations(Ydr) after in-vitro irradiation with 131I and whole blood culture showed the linear-quadratic dose-response equation(Ydr=0.0672 D2-0.1576D + 0.0937). Leucocyte, lymphocyte and platelet counts showed their maximal decrease during weeks at four to six weeks post-irradiation, and returned to normal counts up to three months later. The maximal percentage fall in lymphocyte levels correlated with the administered 131I dosage per unit of body weight (r=0.52, P<0.01). Ydr values had usually increased within two weeks of 132I therapy and were then maintained until at least week eight. Both the maximal-and second week-Ydr value correlated with the administered 131I activity per unit of body weight(r=0.41, p<0.05; r=0.64, p<0.001, respectively). The maximal percentage fall in lymphocyte levels was correlated with the second week-Ydr value(r=0.39, p<0.05). The average total body activity retained at 48 hour was 26.34%. Average absorbed doses to whole blood were 56.54±13.02 rad in the 3.7GBq group, 76.83±19.97 rad in the 5.55GBq, and 95.08±25.51 rad in the 7.4GBq; there was thus significant inter-group correlation(r=0.99,np<0.005). In 131I therapy for thyroid cancer, the second week-Ydr value was the most appropriate early predictor of the effective radiation dose. The linear-quadratic dose-response relationship between radioiodine absorbed dose and the frequency of chromosomal aberrations, which correlate with radioiodine(i.e., at low dose rates) is less carcinogenic than low-dose irradiation with external radiation(i.e., at high dose rates).
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KEYWORD
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Biological dosimetry, In-vitro, Iodine-131, Thyroid carcinoma
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