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Efficiencies are shown relative to the efficiency obtained for the BEAMnrc default case. Springer-Verlag, Heidelberg,anual. The mean energy, planar fluence, and angular and spectral distributions were used as quantities of interest and the estimate of the uncertainty was calculated in five different ways, i.
An additional phantom with a 5 cm air gap embedded in heamnrc was also simulated for dose computations. Once it leaves the forcing zone, the unscattered photon may interact again, depending on the sampled path length.
Please review our privacy beamnr. If the fluence distributions were reconstructed using equal area scoring zones e. The three options for bremsstrahlung photon splitting were used in this study, i. Table 2 Bremsstrahlung splitting techniques and the values used for the relevant parameters. The photon forcing technique produces more photons, however, they are not statistically bezmnrc, thus yielding a lower efficiency although the corresponding PHSP file is generated the fastest.
Estimates of the uncertainty using a significant number of bins e. For a particular efficiency enhancing technique used in BEAMnrcthe difference between the relative efficiencies obtained using the various estimates of the uncertainty increases as one changes from planar fluence to spectral distribution; this situation is clearly more evident for the larger field size see Figs. A photon manusl to interact is split into a scattered photon whose weight is equal to the probability of interaction and an unscattered photon carrying the remaining weight.
All MC simulations were performed on a 2.
BEAMnrc: software tool to model radiation beams – National Research Council Canada
The default differential cross section for the bremsstrahlung interactions is Bethe—Heitler BH. However, as demonstrated in Sec. Here, we investigate the efficiency enhancing methods and cross-section data available in the BEAMnrc MC code system and their effect on the accuracy of calculated fluence and dose distributions. This occurs because of particle correlations which are introduced with the use of VRTs, such as bremsstrahlung splitting.
The parameter values chosen for the different techniques are recommendations from previous published works 1930 or are considered to be reasonable estimates, based on information from the BEAMnrc developers.
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VRTs do not change the physics and therefore do not bias the results. Photon interaction forcing With photon interaction forcing, the user can force photons to interact up to a user-defined number beamhrc times, Nin specified component modules within a simulation.
For the first three uncertainty calculations, only one bin is considered, i.
A 12 195— Although significant differences in the mean energy, planar fluence, and angular and spectral distributions were observed when beammrc the NIST and BH bremsstrahlung cross-section PHSP files, they were not reflected in the calculated dose distribution in a water phantom with and without an air gap.
For both field sizes, the results are presented in Gy per incident particle.
Data Tables 20 2— ; For both field sizes, the results were normalized to the linac calibration point in cGy per MU, i. On the other hand, if one is interested in the most efficient PS simulation note that efficiency is the inverse product of msnual and timemanuwl it is necessary to use VRTs.
When changing the bremsstrahlung differential cross section from BH to NIST, the default photon cross section was used, i. Augmented range rejection accounts correctly for bremsstrahlung production, since charged particles surviving Russian Roulette and with their weight increased by a factor of NBRSPL still have a chance to undergo bremsstrahlung events.
BEAMnrc: software tool to model radiation beams
The current version of BEAMnrc allows the user to choose three photon cross sections: The major advantage of using aggressive VRTs is the significant improvement in calculation time without a compromise in the accuracy of the patient dose computation. The percentage difference between measured and a selection of MC calculated central-axis dose profiles is also shown.
CPU time is scaled to that of a single 2. Some of these special-purpose MC codes are being used as a dose engine for MC-based treatment planning in the routine clinical setting.
National Center for Biotechnology InformationU. The uncertainty was calculated in five different ways, i.