Comparison of cell repair mechanisms by means of chromosomal aberration induced by proton and gamma irradiation – preliminary results

Abstract

Abstract. DNA damage of peripheral blood lymphocytes exposed to gamma and proton irradiation is studied by means of chromosome aberrations to validate the efficiency of the repair mechanisms of individual cells. A new method based on an observed deviation from the Poisson statistics of the chromosome aberration number is applied for estimation of a repair factor (RF ) defined as a ratio between originally damaged cells to the amount of finally observed aberrations. The repair factors are evaluated by studying the variance of individual damage factors in a collective of healthy persons at a given dose as well as by using the chi-square analysis for the dose-effect curves. The blood samples from fifteen donors have been irradiated by Co60 gamma rays and from nine persons by 150 MeV protons with different doses up to 2 Gy. A standard extraction of lymphocyte has been used whereby dicentrics, acentrics and rings have been scored under a microscope. The RF values determined for the proton radiation are slightly larger than for gamma rays, indicating that up to 70% DNA double strand breaks can be repaired.

Fano Factor of Chromosome Aberrations and Asessment of Repair Efficiency

“…1) are overestimated in comparison to the dispersion of data points around the fitted dose-response (225) curve [6]. In the case of the Poisson statistics, about one third of the points should be away from the fitted (according to the linear-quadratic LQ model) curve.…”

“…Overestimation of the variance may be explained by the occurrence of highly efficient repair mechanisms [6,7] which reduces originally produced damage yield Y 1 which could be observed in the lack of any repair. Finally detected aberration yield Y is the result of a decrease of the number of originally induced DNA double strand breaks due to the DNA repair processes.…”

“…We have proposed a new statistical method to study the efficiency of repair mechanisms [6,7] which is based on the estimation of the deviation from the Poisson distribution observed for the dose-effect curves and applicable for relatively low doses at which multiple aberrations are difficult to observe. According to the proposed method, the ratio between the variance and the mean value of the observed aberration distribution is directly related to the efficiency of the cellular repair mechanisms.…”

Radiation dose–response curves: cell repair mechanisms vs. ion track overlapping

“…For example, the tissue specific linear-quadratic (LQ) parameters determined for photon irradiation enabled to predict the RBE of protons [12]. Fitted parameters of CA dose-response curves and statistical distributions of CA [13] have lately allowed to extract some information about physical and biological mechanisms, as well.…”

Nano-scale processes behind ion-beam cancer therapy

“…The papers devoted to these topics are not in this issue because this is a physics journal, while the effects are biological. The previous volume, however, featured references [52,53].…”