Dose Rate Effect of Pulsed Electron Beam on Micronucleus Frequency in Human Peripheral Blood Lymphocytes

Abstract

The micronucleus assay in human peripheral blood lymphocytes is a sensitive indicator of radiation damage and could serve as a biological dosimeter in evaluating suspected overexposure to ionising radiation. Micronucleus (MN) frequency as a measure of chromosomal damage has also extensively been employed to quantify the effects of radiation dose rate on biological systems. Here we studied the effects of 8 MeV pulsed electron beam emitted by Microtron electron accelerator on MN induction at dose rates between 35 Gy min -1 and 352.5 Gy min -1 . These dose rates were achieved by varying the pulse repetition rate (PRR). Fricke dosimeter was employed to measure the absorbed dose at different PRR and to ensure uniform dose distribution of the electron beam. To study the dose rate effect, blood samples were irradiated to an absorbed dose of (4.7±0.2) Gy at different rates and cytogenetic damage was quantifi ed using the micronucleus assay. The obtained MN frequency showed no dose rate dependence within the studied dose rate range. Our earlier dose effect study using 8 MeV electrons revealed that the response of MN was linear-quadratic. Therefore, in the event of an accident, dose estimation can be made using linear-quadratic dose response parameters, without adding dose rate as a correction factor. Arh Hig Rada Toksikol 2010;61:77-83 The micronucleus (MN) assay has been suggested as a reliable alternative method to scoring chromosome aberrations such as dicentrics and rings (1, 2). It allows for the screening of much larger numbers of cells. Furthermore, MN in cytokinesis-blocked binucleated lymphocytes have been used to quantitatively assess the absorbed dose in cases of suspected radiation exposure and situations involving radiation accidents (3). The dose-response curve of MN frequency in peripheral blood lymphocytes induced by low linearenergy-transfer (LET) radiations is best described by linear-quadratic function (4-7). The slope of the dose-response curve, which represents a numerical measure of aberrations induced by single radiation track events, is usually independent of the dose rate. KEY WORDS: dosimetry, microtron, 8 MeV electrons, pulse repetition rate Acharya S, et al. PULSED ELECTRON BEAM DOSE RATE EFFECT ON MN FREQUENCYThe quadratic component that refers to an interaction between effects from two or more independent tracks is dose rate dependent, and its magnitude depends on the time interval between the two tracks (8).The dose rate effect of radiation is a biophysical phenomenon and is a consequence of repair of sublethal damage. Several earlier studies have suggested that even though it is quite obvious that radiobiological damage decreases with the dose rate, this does not work the other way around when the dose rate rises above a certain level (5, 9-11). However, there are conflicting reports regarding the dose rate effect studied in different types of cells (12-15).Our earlier dose-effect study using 8 MeV electrons revealed that the response of MN was linear-quadratic Unauthenticated Download ...