Use of a radial projection to reduce the statistical uncertainty of spot lateral profiles generated by Monte Carlo simulation

Abstract

Monte Carlo (MC) simulation has been used to generate commissioning data for the beam modeling of treatment planning system (TPS). We have developed a method called radial projection (RP) for postprocessing of MC‐simulation‐generated data. We used the RP method to reduce the statistical uncertainty of the lateral profile of proton pencil beams with axial symmetry. The RP method takes advantage of the axial symmetry of dose distribution to use the mean value of multiple independent scores as the representative score. Using the mean as the representative value rather than any individual score results in substantial reduction in statistical uncertainty. Herein, we present the concept and step‐by‐step implementation of the RP method, as well as show the advantage of the RP method over conventional measurement methods for generating lateral profile. Lateral profiles generated by both methods were compared to demonstrate the uncertainty reduction qualitatively, and standard error comparison was performed to demonstrate the reduction quantitatively. The comparisons showed that statistical uncertainty was reduced substantially by the RP method. Using the RP method to postprocess MC data, the corresponding MC simulation time was reduced by a factor of 10 without quality reduction in the generated result from the MC data. We concluded that the RP method is an effective technique to increase MC simulation efficiency for generating lateral profiles for axially symmetric pencil beams.

Technical Note: Comprehensive evaluation and implementation of two independent methods for beam monitor calibration for proton scanning beam

“…This means that the relative differences of the DAPs determined by the two independent methods are independent of the large field sizes of 20 or 40 cm. Small changes (~0.2%) in CSCF and FSCF from 20 to 40 cm were derived from high precision Monte Carlo simulations . The practical concern on selecting a large field size such as 40 cm is that the large field would require a much longer time to deliver the desired dose, and more importantly, these small differences may not be measurable because they are smaller than the uncertainty of the dosimetry system.…”

“…Small changes (~0.2%) in CSCF and FSCF from 20 to 40 cm were derived from high precision Monte Carlo simulations. 22 The practical concern on selecting a large field size such as 40 cm is that the large field would require a much longer time to deliver the desired dose, and more importantly, these small differences may not be measurable because they are smaller than the uncertainty of the dosimetry system. Nevertheless, Palmans and Vatnisky 9 stated that these very low but widely extended dose tails are contributions from neutrons and gammas rays, and the dose contribution to realistic size patients are negligible.…”

Clinical Validation of a Ray-Casting Analytical Dose Engine for Spot Scanning Proton Delivery Systems

“…The DE1 was commissioned using data generated by an MC code 34 based on the Geant4 10.0 release. [35][36][37] The geometry of the PBS nozzle in the MC simulation was matched to the design configuration provided by the vendor and the vendorprovided data.…”

Feasibility of using megavoltage computed tomography to reduce proton range uncertainty: A simulation study

“…To calculate CT numbers for kV and MV beams, simulation code based on Geant4 (Geant4 Collaboration, https://geant4.web.cern.ch/) was developed to obtain phase‐space files behind the phantom, for an infinitively small photon beamlet 19,20 at 60 keV or 0.8 MeV. For each run, the phantom was filled with a single type of material, either water or one of the 32 reference human tissues as defined in Table 1.…”