Comparison of Biophysical and Radiological Responses of Bio-Test Objects to Pulsed and Continuous X-Ray and Neutron Irradiations

Aims: To correlate qualitatively and quantitatively biological effectiveness of irradiations of bio-test objects by neutrons, X- and gamma-rays within a wide range of doses, dose rates (dose powers), durations of action and spectral contents of the radiations.

Study Design: These irradiations were done with the help of well-known and newly elaborated sources of the above radiations based on isotopes, fission reactors, X-ray tubes and Dense Plasma Focus (DPF) devices.

Place and Duration of Study: Institute of Metallurgy and Material Science (IMET), Institute of Plasma Physics and Laser Microfusion (IPPLM), Moscow State University (MSU), and Medical Radiological Research Center (MRRC), between June 2007 and December 2011.

Methodology: As biological test objects of different contents and complexity we used enzymes of various types, serum, seminal fluid, human lymphocytes. Enzymes activity prior to and after irradiation was measured using spectrophotometer (Hitachi) within the wavelength range Δl = 300÷750 nm according to up-to-date techniques. In the comparative researches the cytogenetic action of fission neutrons (generated by nuclear reactors) and of fusion 14-MeV neutrons (from DPF) were studied with the most widespread test-system – chromosomal aberrations in human lymphocytes.

Results: The range of the variations of the coefficient of biological effectiveness for neutron radiation of dissimilar dose rates (dose powers) and neutron spectra as a rule does not go out from the limits of physiological oscillations at the neutron dose power that changes within 9 orders of magnitude (till the figure 108 Gy/min) and it coincides with the “classic” dose rate effect (a quadratic part of dose curves for cell survival or chromosomal aberrations). Yet in the field of radioenzymology the very powerful X-ray radiation results in activation or suppression of enzymes at doses differing by 4-5 orders of magnitude (to lesser doses) compared with analogous effects obtained with low power isotope and X-ray tube sources.

Conclusion: Resemblance of neutron action on dose powers within 9 orders of magnitude gives hope of applicability of the DPF neutron generators for the potential methods of neutron therapy instead of dangerous, expensive and cumbersome nuclear reactors. But the anomalously strong X-ray influence upon enzymes dictates careful application of super-high power X-ray pulses and demands further investigations of the nature of these effects.