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Large efficiency improvements in BEAMnrc using directional bremsstrahlung splitting
Author(s) -
Kawrakow I.,
Rogers D. W. O.,
Walters B. R. B.
Publication year - 2004
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1788912
Subject(s) - bremsstrahlung , beam (structure) , fluence , photon , dosimetry , imaging phantom , optics , physics , compton scattering , materials science , nuclear physics , atomic physics , irradiation , nuclear medicine , medicine
The introduction into the BEAMnrc code of a new variance reduction technique, called directional bremsstrahlung splitting (DBS), is described. DBS uses a combination of interaction splitting for bremsstrahlung, annihilation, Compton scattering, pair production and photoabsorption, and Russian Roulette to achieve a much better efficiency of photon beam treatment head simulations compared to the splitting techniques already available in BEAMnrc (selective bremsstrahlung splitting, SBS, and uniform bremsstrahlung splitting, UBS). In a simulated 6 MV photon beam ( 10 × 10cm 2field) photon fluence efficiency in the beam using DBS is over 8 times higher than with optimized SBS and over 20 times higher than with UBS, with a similar improvement in electron fluence efficiency in the beam. Total dose efficiency in a central‐axis depth‐dose curve improves by a factor of 6.4 over SBS at all depths in the phantom. The performance of DBS depends on the details of the accelerator being simulated. At higher energies, the relative improvement in efficiency due to DBS decreases somewhat, but is still a factor of 3.5 improvement over SBS for total dose efficiency using DBS in a simulated 18 MV photon beam. Increasing the field size of the simulated 6 MV beam to 40 × 40cm 2(broad beam) causes the relative efficiency improvement of DBS to decrease by a factor of ≈ 1.7 but is still up to 7 times more efficient than with SBS.