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Description of Energy Dose Deposition Kernel for the Diagnostic Beam

r kareem*, M Liebmann, N Chofor, T Luellau, B Poppe, Carl von Ossietzky University & Pius-Hospital Oldenburg, Germany

SU-E-I-106 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Tover the recent years, the employment of kV x-rays as a diagnostic tool into clinical routine has resulted in a significant increase in the patient's exposure to ionizing radiation. The accurate determination of the absorbed dose to patients during diagnosis is therefore necessary to avoid unnecessary exposure to the patient. This study presents an analytical model of the energy deposition kernel for the monoenergetic and poly-energetic kV beams for the fast calculation of dose in radiography. Methods: The analytical model is based on the pencil beam kernels derived from Monte Carlo simulations. DOSXYZnrc code from the EGSnrc family was employed to simulate the pencil beam of 0.1 cm width for 80, 100 and 120 keV mono-energetic and polyenergetic beams. The lateral dose profiles were calculated at different depths within a homogenous water phantom of size 50x50x50 cm³. The evaluated dose profiles showed a high amplitude primary component at the central axis and a long range low amplitude scatter component spanning a considerable distance from the central axis. The profiles were fitted analytically with a triple exponential decay function with an offset. All coefficients of the exponential function were further fitted with appropriate analytical functions to represent their behavior relative to depth and photon energy. The accuracy of the obtained kernel was checked by the convolution of a rectangular fluence profile and comparing the calculated dose distribution with the Monte Carlo simulated dose profiles for 2x2 cm² field size. Results and Conclusion: In a homogeneous phantom, the comparisons of the convolution method and Monte Carlo simulations showed sufficient agreement except for largest depths (deviation approx. 15%). Future developments will focus on an implementation of the method for dose calculation in the patient.

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