Induction of chromosome aberrations in human lymphocytes by technetium-99m. In vitro and in vivo studies

INTRODUCTION Research on the effects of low-dose exposure to ionizing radiation in human has been widely studied. In diagnostic Nuclear Medecine, calculated doses delivered to whole-body and organs were very low (1) and scintigraphies are considered as safe. Consequently only a few studies concerning the potential biological and genetic effects of radiopharmaceutical administration have been carried out (2, 3) The aim of this study was to evaluate the potential cytogenetic effects of exposure to a clinical dose of technetium 99m (99mTc). The induction by ionizing radiations of unstable structural chromosome aberrations (dicentrics, ring and excess acentric fragments) in peripheral blood lymphocytes is considered to be a useful technique to complete physical dosimetry, and presently is the most sensitive biological method to monitor human radiation exposure (4). A specific relationships between activty of 99mTc and number of unstable chromosomal aberration was established in vitro. At our knowledge, such relationships have never been performed with this radioisotope. However, the scoring of chromosome aberrations in human lymphocytes varied with effects of radiation quality, dose and dose rate (5). In this context, whole blood samples from healthy donors were irradiated by external 99mTc source and frequency of unstable chromosomal aberrations versus activity of 99mTc was assessed using conventional cytogenetic technique. Unstable chromosome aberrations in peripherical blood lymphocytes from 5 patients exposed to a 99mTc for bone scintigraphy were also examinated. In vitro and in vivo results of unstable aberration scoring were compared. Stable aberration scoring (translocations) performed on the same in vivo and in vitro irradiated blood sample are actualy being carried out in our laboratory, to evaluate the potential genetic risk of 99mTc exposure. Primilary stable aberration scoring are also presented.