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This article has been beamnfc by other articles in PMC. Table 2 Bremsstrahlung splitting techniques and the values used for mnaual relevant parameters. 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. An investigation of the influence of different photon and bremsstrahlung cross-section data available in BEAMnrc on the accuracy of calculated fluence and dose distributions.
The CPU times were scaled to a single 2. Springer-Verlag, Heidelberg,pp. Boundary crossing algorithm The boundary crossing algorithm together with the electron transport algorithm constitutes the condensed history technique used by a particular MC code system.
The uncertainty was calculated in five different ways, i. For both field sizes, the results are presented in Gy per incident particle.
The percentage difference, in the central region of the field and at different depths, between the two MC calculated data is also shown. Efficiencies are shown relative to the efficiency obtained for the BEAMnrc default case. The percentage difference between the two MC calculations is also shown.
BEAMnrc, DOSXYZnrc and BEAMDP GUI users manual – NRC Publications Archive –
This is a technique, recently introduced in BEAMnrc18 that is more efficient than the standard range rejection scheme just described. The percentage difference between the two MC calculated data is also shown.
The two MC programs generate accurate PHSP files of the linear accelerator for mmanual planning bramnrc dosimetric verification purposes in a relatively short amount of time when the appropriate efficiency enhancing tools are used.
Therefore, if one is concerned with the smallest statistical uncertainty variance in dose, then it is best to perform the treatment head PS simulation without VRTs. It is important to correctly manuao a measure of the overall uncertainty on the quantity of interest in order to accurately evaluate the efficiency of a particular MC simulation algorithm. Photon and bremsstrahlung cross sections The current version of BEAMnrc allows the user to choose three different photon cross sections: On the other manal, the scattered photon can be forced to interact again in the forcing zone, depending on how many forced interactions are still available.
When using UBS, each bremsstrahlung event produces a predefined number of bremsstrahlung photons, each having a weight equal to the inverse of the splitting number NBRSPL times the weight of beqmnrc electron that underwent the bremsstrahlung event.
Data Tables 20 2— ; Data Tables 7 6— The current version of BEAMnrc allows the user to choose three photon cross sections: Variance reduction techniques Bremsstrahlung photon splitting, Russian Roulette, and electron splitting The three options for bremsstrahlung photon splitting were used in this study, i.
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Academic, New York,Vol. This work was supported in part by Grant Nos. If one uses VRTs e. The boundary crossing algorithm together with the electron transport algorithm constitutes the condensed history technique used by a particular MC code system. Although significant differences in the mean energy, planar fluence, and angular and spectral distributions were observed when comparing 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.
Once it leaves the forcing zone, the unscattered photon may interact again, depending on the sampled path length. However, as demonstrated in Sec. Russian Roulette was also considered with the photon splitting techniques. 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 use of sophisticated variance reduction and approximate efficiency improving techniques, combined with parallel processing in computer clusters and the continuing increase in computing power, will help bea,nrc MC-based treatment planning a mainstay option in radiation oncology departments. Published besmnrc Nov 5.
CPU time is scaled to that of a single 2. The percentage difference between measured and a selection of MC calculated central-axis dose profiles is also shown. VRTs do not change the physics and therefore do not bias the results. An additional phantom with a beamnrd cm air gap embedded in water was also simulated for dose computations.
BEAMnrc: software tool to model radiation beams
It has been reported that this option increases the efficiency of homogeneous phantom calculations, 38 however, no photon splitting or charged particle range rejection were employed. In addition, the methods for performing the efficiency and statistical uncertainty calculations are described. A systematic study of the influence of efficiency enhancing methods available in BEAMnrc on the accuracy of calculated fluence and dose distributions.
In the megavoltage energy range, there are small but observable differences between the two differential cross sections refer to Fig. A 12 195— A 3— Support Center Support Center. With SBS, the value of NBRSPL is changed in order to maximize the splitting of photons beamnnrc into the field and to minimize unnecessary splitting of photons aimed away from the field.
Manuall photon splitting was used together with the other techniques, only the cases with improved photon and electron fluence were manial, i. Medical Physics, Windsor,pp. The electron and photon cutoff energies were set to 0.
Monte Carlo, efficiency, variance reduction techniques, cross sections. The tradeoff is that the no-VRT simulation is much slower, although if this simulation is being performed just once for subsequent use then it is a reasonable approach. Augmented charged particle range rejection is only available when used simultaneously with Msnual. Augmented range rejection accounts correctly for bremsstrahlung production, since charged particles surviving Russian Roulette and with their weight increased by a factor bfamnrc NBRSPL still have a chance to undergo bremsstrahlung events.