APENELOPE‐based system for the automated Monte Carlo simulation of clinacs and voxelized geometries—application to far‐from‐axis fields

Medical Physics - Tập 38 Số 11 - Trang 5887-5895 - 2011
Josep Sempau1,2, Andreu Badal3, L. Brualla4
1Electronic mail: [email protected]
2Institut de Tècniques Energètiques, Universitat Politècnica de Catalunya, Diagonal 647, E-08028 Barcelona, Spain
3Division of Imaging and Applied Mathematics, OSEL, CDRH U.S. Food and Drug Administration, 10903 New Hampshire Ave, Silver Spring, Maryland 20993-0002
4NCTeam, Strahlenklinik, Universitätsklinikum Essen, Hufelandstr. 55, D-45122 Essen, Germany

Tóm tắt

Purpose:Two new codes,PENEASYandPENEASYLINAC, which automate the Monte Carlo simulation of Varian Clinacs of the 600, 1800, 2100, and 2300 series, together with their electron applicators and multileaf collimators, are introduced. The challenging case of a relatively small and far‐from‐axis field has been studied with these tools.Methods:PENEASYis a modular, general‐purpose main program for thePENELOPEMonte Carlo system that includes various source models, tallies and variance‐reduction techniques (VRT). The code includes a new geometry model that allows the superposition of voxels and objects limited by quadric surfaces. A variant of the VRT known as particle splitting, called fan splitting, is also introduced.PENEASYLINAC, in turn, automatically generates detailed geometry and configuration files to simulate linacs withPENEASY. These tools are applied to the generation of phase‐space files, and of the corresponding absorbed dose distributions in water, for two 6 MV photon beams from a Varian Clinac 2100 C/D: a 40 × 40 cm2centered field; and a 3 × 5 cm2field centered at (4.5, −11.5) cm from the beam central axis. This latter configuration implies the largest possible over‐traveling values of two of the jaws. Simulation results for the depth dose and lateral profiles at various depths are compared, by using the gamma index, with experimental values obtained with a PTW 31002 ionization chamber. The contribution of several VRTs to the computing speed of the more demanding off‐axis case is analyzed.Results:For the 40 × 40 cm2field, the percentages γ1and γ1.2of voxels with gamma indices (using 0.2 cm and 2% criteria) larger than unity and larger than 1.2 are 0.2% and 0%, respectively. For the 3 × 5 cm2field, γ1 = 0%. These figures indicate an excellent agreement between simulation and experiment. The dose distribution for the off‐axis case with voxels of 2.5 × 2.5 × 2.5 mm3and an average standard statistical uncertainty of 2% (1σ) is computed in 3.1 h on a single core of a 2.8 GHz Intel Core 2 Duo processor. This result is obtained with the optimal combination of the tested VRTs. In particular, fan splitting for the off‐axis case accelerates execution by a factor of 240 with respect to standard particle splitting.Conclusions:PENEASYandPENEASYLINACcan simulate the considered Varian Clinacs both in an accurate and efficient manner. Fan splitting is crucial to achieve simulation results for the off‐axis field in an affordable amount of CPU time. Work to include Elekta linacs and to develop a graphical interface that will facilitate user input is underway.

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Medical Physics

Tập 38 Số 11

5887-5895

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