Cytogenetic effects of radioiodine therapy: a 20-year follow-up study

Abstract

The purpose of this study was to compare cytogenetic data in a patient before and after treatment with radioiodine to evaluate the assays in the context of biological dosimetry. We studied a 34-year-old male patient who underwent a total thyroidectomy followed by ablation therapy with (131)I (19.28 GBq) for a papillary thyroid carcinoma. The patient provided blood samples before treatment and then serial samples at monthly intervals during the first year period and quarterly intervals for 5 years and finally 20 years after treatment. A micronucleus assay, dicentric assay, FISH method and G-banding were used to detect and measure DNA damage in circulating peripheral blood lymphocytes of the patient. The results showed that radiation-induced cytogenetic effects persisted for many years after treatment as shown by elevated micronuclei and chromosome aberrations as a result of exposure to (131)I. At 5 years after treatment, the micronucleus count was tenfold higher than the pre-exposure frequency. Shortly after the treatment, micronucleus counts produced a dose estimate of 0.47 ± 0.09 Gy. The dose to the patient evaluated retrospectively using FISH-measured translocations was 0.70 ± 0.16 Gy. Overall, our results show that the micronucleus assay is a retrospective biomarker of low-dose radiation exposure. However, this method is not able to determine local dose to the target tissue which in this case was any residual thyroid cells plus metastases of thyroidal origin.

Cytogenetic Biomarkers of Radiation Exposure

“…In unknown or mixed dose exposure scenarios this may not always be the case. For instance, uncertainties in estimating cancer risks from the neutron component for A-bomb survivors, the potential for internal radionuclide contamination for nuclear workers and from nuclear fallout and, in assessing risks for medical workers exposed to radioactive isotopes [1,2]. Expressed in units of keV/m, LET specifies the average energy transferred per unit length of the track and correspondingly differentiates sparsely (e.g.…”

Cytogenetic Studies of Chromosome Abnormalities in Thyroid Cancer Patients Before and After Iodine-131 Treatment

“…Since patients receiving treatment were exposed to harmful effects of gamma rays and beta rays directly affecting tissue, analyses were made to determine chromosome damage in peripheral blood before and after treatment. As in our study, the reasons for choosing peripheral blood as material to examine the effects of the IR are that lymphocytes are highly sensitive to the IR, circulate through the entire body and are numerous, it easy to obtain them and short-term culture techniques are easy to apply (9,11).…”

“…The examination of chromosomal breakages and SCE, which are indicators of chromosome instability, by various methods are the most effective methods used to determine the damage to cells (10). The loss of genomic stability resulting from gene rearrangement, leading to the formation of different types of cancer and at the same time, increasing the risk of secondary cancers seen after the treatment of cancer is one of the most important pathological stages (11). I-131 has been used in medical field for diagnosis and treatment since 1942 (17).…”

“…Although there are long-term studies on chromosomal abnormalities of individuals exposed to high doses of radiation, long-term studies on cytogenetic effects of low doses of IR exposure for diagnosis and treatment purposes are limited. Livingston et al (11) followed up cytogenetic findings in a patients who underwent total thyroidectomy and ablation treatment, at certain intervals by taking peripheral blood for 20 years. The results showed that cytogenetic effects persisted after treatment due to I-131 exposure.…”

“…Small errors are mostly repaired by DNA repair systems, while severe errors stimulate apoptosis, leading the cell to death. The accumulation of errors in the cell is the first step of carcinogenesis, causing mutations (11).…”