Microdosimetry-Based Characterisation of X-Ray Irradiators and Dose Enhancement Factor Study for Cell Monolayer Irradiation

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Abstract: This paper presents the results of computer modeling aimed at determining the quality characteristics of the widely used in radiobiological research photon beams. Particularly, $^{60}$Co and X-ray irradiators, such as SARRP, X-RAD 320, CellRad and Seifert are commonly used photon sources for in vitro irradiation of biological samples. The X-ray spectra were calculated using the SpekPy code and used for further calculations in the Monte Carlo (MC) PHITS code, which includes specialised track-structure mode for particle transport. PHITS was used to simulate typical conditions of irradiation of a cell monolayer, particularly, lymphocytes, and the necessary microdosimetric characteristics were determined, as well as the average values of linear energy transfer (LET). Based on the results obtained during the simulations, the Relative Biological Effectiveness (RBE) is calculated within the Theory of Dual Radiation Action (TDRA) and the Microdosimetric Kinetic model (MKM) frameworks. The contribution of various photon interaction processes to the total absorbed dose in the sample has been studied. The article discusses the influence of irradiation conditions, examines the effect of cell monolayer covering and the possible dose increase associated with it. The simulation results emphasize the importance of the irradiation conditions used. In particular, using cover glass on cell monolayer during X-ray irradiation shows an increase in the dose by a factor of 2.