A cytogenetic approach to the effects of low levels of ionizing radiations on occupationally exposed individuals

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Abstract

The aim of the present study was to assess occupationally induced chromosomal damage in hospital workers exposed to low levels of ionizing radiation. Thirty-two interventional cardiologists, 36 nuclear medicine physicians and 33 conventional radiologists were included in this study, along with 35 healthy age- and sex-matched individuals as the control group. We used conventional metaphase chromosome aberration (CA) analysis, cytokinesis-block micronucleus (MN) assay as important biological indicators of ionizing radiation exposure. Occupational dosimetry records were collected over the last year (ranged from 0.25 to 48 mSv) and their whole life exposure (ranged from 1.5 to 147 mSv). The results showed significantly higher frequencies of dicentric and acentric CAs (p < 0.001) and MN (p < 0.01) in all exposed groups than in the controls. Taking all the confounding factors into account, no obvious trend of increased chromosomal damages as a function of either duration of employment, exposed dose, sex or age was observed. Interventional cardiologists had the highest rates of CA and MN frequencies between the worker groups, though the differences were not significant. These results indicate that long term exposure to low dose ionizing radiation could result in DNA damage. Hence, the personnel who work in the hospitals should carefully apply the radiation protection procedures.

Introduction

The latest UNSCEAR [1] reports that of all workers exposed worldwide to man-made sources of radiation, medical radiation workers represent the largest group and they are most consistently exposed to low doses of ionizing radiations. Health risks from radiation exposure in such a large occupational segment of the population are clearly of special concern. Levels of exposure to ionizing radiation in hospitals have decreased in recent decades and are now far below the regulatory limit of 20 mSv/year, however, some medical uses of radiation, such as nuclear medicine and interventional procedures, may expose personnel to higher doses, and these are subjects of concern. Moreover, personal dosimetry may underestimate the real exposure, not only because of the detection threshold of dosimeters but also because of improper wearing.

Diagnostic radiology, especially interventional cardiac procedures can deliver high radiation doses to the clinical staff. Staff exposure rates associated with the examination rooms can be 2 mGy h−1 or more, depending on location and fluoroscopic technique. Cardiac catheterization, in particular, can constitute a source of relatively high exposure [2]. This exposure may represent a significant health risk, resulting in deleterious clinical implications that can affect not only the personnel involved but also their progeny.

On the other hand, medical personnel occupied in nuclear medicine departments also are occupationally exposed to low doses of ionizing radiation. Exposure may occur during the handling of radioactive material, in the process of application of radioactive material to patients, from the patient subjected to application of radioactive material and by contamination. While external contamination usually arises as a result of an accidental exposure, internal contamination may not be practically avoidable in certain occupations. Internal intake can result from the inhalation of radionuclides in air, ingestion or absorption through skin [3].

Monitoring of personnel occupationally exposed to ionizing radiation consists of regular film dosimetric control and periodic health examination. Cytogenetic studies as specific biological parameters provide additional information which complements physical dosimetry and enables better evaluation of radiation health effects. Analysis of chromosomal aberrations (CAs) and other cytogenetic biomarkers such as micronucleus (MN) in peripheral blood lymphocytes have also been used for a long time for the evaluation of exposures to various mutagens or carcinogens.

CAs, especially dicentrics, induced by ionizing radiation in human lymphocytes provides the most sensitive and reliable method for biological dosimetry [4]. Many papers have been published studying the effects of low level radiation for the occupationally exposed hospital workers by means of conventional metaphase chromosome analysis [5], [6]. Although the baseline frequency of CAs from the normal population has a wide range of variation which might reflect interlaboratory differences in culture conditions or sample characteristics, it is evident that in all individuals exposed to ionizing radiation in the above mentioned studies, higher frequency of CAs was reported compared to control, even if their exposure was lower than permissible level.

Another cytogenetic assay used for biodosimetry is the scoring of micronucleus formation. There are many reports of increased frequency of MN in occupationally exposed individuals in hospitals [7], [8].

Even when occupational exposure is far below the limits set by ICRP or legislation, they should not be disregarded. The aim of the present study was to perform a cytogenetic analysis in peripheral lymphocytes of three groups of hospital workers who had no dosimetrically recorded exposure dose higher than permissible level in their duration of work and compare the results with control individuals, using the cytogenetic end points of CAs and MN.

Section snippets

Study population

The study was carried out in three groups of professional radiation workers in Iran hospitals; 32 interventional cardiologist (group A), 36 nuclear medicine physicians (group B) and 33 conventional radiologists (group C) and the results were compared with 35 age- and sex-matched control group. These persons had been occupationally exposed to different radiation sources from 2 to 20 years and their ages ranged between 28–52 years. Concerning the occupational radiation dose, the official personal

RESULTS

Demographic characteristics of control and exposed workers are presented in Table 1. The control and exposed subjects did not significantly differ in age, sex and smoking habits.

The results of chromosomal analyses in the radiation workers and controls are presented in Table 2.

Both types of acentric and dicentric CA frequencies were significantly (p < 0.001) increased among workers (Table 2). The acentric and dicentric chromosomal aberration frequencies per 100 cells in three groups of workers (A,

Discussion and conclusion

In this study, two cytogenetically different endpoints, i.e., chromosomal aberrations and micronucleus assay were used to detect the effects of chronic exposure of low levels of ionizing radiation to hospital workers in interventional cardiology, conventional radiology and nuclear medicine centers. In this study, occupational dosimetry records over the last year ranged from 0.25 to 48 mSv and were within the limit established by the ICRP [2], and their whole life exposure ranged from 1.5 to 147 

References (25)

  • UNSCEAR, United Nations Scientific Committee on the Effects of Atomic Radiation. Ionizing radiation: sources and...
  • ICRP, International Commission on Radiological Protection. Radiation and your patient: a guide for medical...
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