论文信息 - Comparisons of thick-target bremsstrahlung calculations by EGS4/PRESTA and ITS version 2.1

Comparisons of thick-target bremsstrahlung calculations by EGS4/PRESTA and ITS version 2.1

Abstract Two Monte Carlo codes, EGS4/PRESTA and ITS version 2.1, have been used to calculate spectral distributions of bremsstrahlung and annihilation quanta in 10–30 MV beams from thick targets of Be, Al, and Pb. Spectra are absolute (photons per incident electron) and calculated in 44 annular regions of 1° widths, covering all angles. It was found necessary to do ITS calculations using shortened sub-step sizes for electrons near the target surface to remove a 30–40% error in the angular distribution of bremsstrahlung at small angles that occurs when using default sub-step sizes. The EGS calculations were done using the enhancement which randomly samples the bremsstrahlung angle from an appropriate distribution and giving due consideration to K-shell X-rays. A survey is done of the remaining discrepencies in the spectral distributions of fluence, the total fluence and the mean energies of each spectrum. In general, EGS and ITS agree to ±20% for fluence and ±5% for mean energy. Results are compared to a set of high-precision measurements of absolute thick-target bremsstrahlung spectra used previously to show that EGS is reliable to ±10% for fluence and ±2% for mean energy. The measurements did not clearly identify a strong preferance towards either EGS or ITS.

David W. O. Rogers | Bruce A. Faddegon | B. Faddegon | D. Rogers

[1] R. C. McCall,et al. Improvement of linear accelerator depth-dose curves. , 1978, Medical physics.

[2] O Sauer,et al. Reconstruction of high-energy bremsstrahlung spectra by numerical analysis of depth-dose data. , 1990, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[3] B A Faddegon,et al. Forward-directed bremsstrahlung of 10- to 30-MeV electrons incident on thick targets of Al and Pb. , 1990, Medical physics.

[4] Martin J. Berger,et al. Bremsstrahlung spectra from electron interactions with screened atomic nuclei and orbital electrons , 1985 .

[5] R Mohan,et al. Energy and angular distributions of photons from medical linear accelerators. , 1985, Medical physics.

[6] D. Findlay. Analytic representation of bremsstrahlung spectra from thick radiators as a function of photon energy and angle , 1989 .

[7] M. A. Lone,et al. Bremsstrahlung and photo-neutron yields from 5-25 MeV electrons on thin slabs of Al, Fe, Cu and Pb , 1985 .

[8] B A Faddegon,et al. Angular distribution of bremsstrahlung from 15-MeV electrons incident on thick targets of Be, Al, and Pb. , 1991, Medical physics.

[9] J. W. Motz,et al. Bremsstrahlung Cross-Section Formulas and Related Data , 1959 .

[10] J. Cunningham,et al. On the selection of stopping-power and mass energy-absorption coefficient ratios for high-energy x-ray dosimetry. , 1984, Medical physics.