254 Pak J Med Sci 2007 Vol. 23 No. 2 www.pjms.com.pk Original Article PERSISTENT UNSTABLE CHROMOSOMAL ABERRATIONS IN LYMPHOCYTES OF RADIOTHERAPY WORKERS AFTER 1 ST MITOTIC DIVISION IN TEHRAN, IRAN Abol f azl Movaf agh 1 , F. Mal eki 2 , S. Fadaie 3 , E. Azar Gashb 4 ABSTRACT Objective: Studies indicate that ionizing radiation can induce persistent genetic instability in a high proportion of exposed cells. It has also been reported that exposure of radiotherapy workers to ionizing radiation causes chromosomal damages. Some of the damaged cells show a large number of aberrations such as dicentrics, polycentrics, rings, and numerous acentric fragments.To determine, whether chromosomal damages can be used as a biomarker of possible radiation in occupational exposure in a hospital setting. Met hodology: In this study, chromosome abnormalities were evaluated in peripheral blood lym- phocytes from fifty medical radiotherapy workers who handled ionizing radiation for an average of twelve years, and forty three control individuals who did not knowingly come in contact with any radiation source. Chromosome aberrations were evaluated by the conventional solid stain t echnique. Result s: Dicentrics, fragments, followed by ring chromosomes, as well as total chromosome aberrations were elevated in the experimental group. We did not observe any aneuploidy chromosome in the present study. Although the level of exposure was below the annual permissible limit of twenty mSv/ y recommended by the International Commission for Radiation Protection for whole body exposure, the mean frequencies of different chromosomal aberrations were higher in radiotherapy workers compared with controls (P=0.041). Although the mean frequencies of chromosomal aberrations in the female workers (3.5±1.42) was slightly higher than in males (3.28±0.95), there was no significant differences (P=0.74) in the frequency of chromosome aberration between males and females of ionizing radiotherapy workers. Conclusion: The results of this study underscore the need of adopting measures to avoid or minimize overexposure to radiation in hospital settings. KEY WORDS : Chromosome, aberration, radiotherapy worker, radiation. Pak J Med Sci April 2007 Vol. 23 No. 2 254-258 1. Dr. Abolfazl Movafagh, 2. Dr. F. Maleki, 3. Dr. S. Fadaie 4. Dr. E. Azar Gashb 1-4: Shahid Beheshti Medical University, Evin Ave. Tehran, Iran. Correspondences: Dr. Abolfazl Movafagh,PhD Associate professor, Shahid Beheshti Medical University, Evin Ave, Tehran Iran E-Mail: movafagh_a@yahoo.com * Received for Publication: May 8, 2006 * Accepted: October 3, 2006 INTRODUCTION Exposure of cells to ionizing radiation pro- duces an extremely wide range of DNA dam- aging and mutational events. DNA double- stranded breaks are generally accepted to be the most biological significant lesion produced by ionizing radiation, and may ultimately re- sult in cancer. 1 All types of ionizing radiation increases numerical chromosome aberrations. 2 Exposure to radiation during the embryonic or pre-embryonic stages increases susceptibility to carcinogens. 3 Chromosome aberration is regarded as be- ing the most sensitive indication of radiation-