Unfiltered Monte Carlo-based tungsten anode spectral model from 20 to 640 kV

A Monte Carlo-based tungsten anode spectral model, conceptually similar to the previously-developed TASMIP model, was developed. This new model provides essentially unfiltered x-ray spectra with better energy resolution and significantly extends the range of tube potentials for available spectra. MCNPX was used to simulate x-ray spectra as a function of tube potential for a conventional x-ray tube configuration with several anode compositions. Thirty five x-ray spectra were simulated and used as the basis of interpolating a complete set of tungsten x-ray spectra (at 1 kV intervals) from 20 to 640 kV. Additionally, Rh and Mo anode x-ray spectra were simulated from 20 to 60 kV. Cubic splines were used to construct piecewise polynomials that interpolate the photon fluence per energy bin as a function of tube potential for each anode material. The tungsten anode spectral model using interpolating cubic splines (TASMICS) generates minimally-filtered (0.8 mm Be) x-ray spectra from 20 to 640 kV with 1 keV energy bins. The rhodium and molybdenum anode spectral models (RASMICS and MASMICS, respectively) generate minimally-filtered x-ray spectra from 20 to 60 kV with 1 keV energy bins. TASMICS spectra showed no statistically significant differences when compared with the empirical TASMIP model, the semi-empirical Birch and Marshall model, and a Monte Carlo spectrum reported in AAPM TG 195. The RASMICS and MASMICS spectra showed no statistically significant differences when compared with their counterpart RASMIP and MASMIP models. Spectra from the TASMICS, MASMICS, and RASMICS models are available in spreadsheet format for interested users.