### Abstract

A photon virtual source model was developed for simulating arbitrary, external beam, intensity distributions using the Monte Carlo method. The source model consists of a photon fluence grid composed of a matrix of square elements, located 25-cm downstream from the linear accelerator target. Each particle originating from the fluence map is characterized by the seven phase space parameters, position (x, y, z), direction (u, v, w), and energy. The map was reconstructed from fluence and energy spectra acquired by modeling components of the linear accelerator treatment head using the Monte Carlo code MCNP4B. The effect of contaminant electrons is accounted for by the use of a sub-source derived from a phase-space simulation of a 25-MV linac treatment head using the code BEAM. The BEAM sub-source was incorporated into the MCNP4B phase-space model and is sampled using a field-size dependent sampling ratio. A Gaussian blurring kernel is convolved with the photon fluence map to account for the finite focal spot size and scattering effects from structures such as the flattening filter and MLC leaves. Depth dose and profile source calculations for 6-MV and 25-MV photon beams, for 5 x 5 cm^{2}, 10x 10 cm^{2}, and 15x 15 cm^{2} field sizes, are in good agreement with measurement and are well within acceptability criteria suggested by the AAPM Task Group Report No. 53. Irregular field calculations compared with film measurement and with a 3-D pencil beam algorithm show that the source model is capable of accurately simulating arbitrary MLC fields.

Original language | English (US) |
---|---|

Pages (from-to) | 166-172 |

Number of pages | 7 |

Journal | Medical Physics |

Volume | 27 |

Issue number | 1 |

DOIs | |

State | Published - Jan 2000 |

### Fingerprint

### Keywords

- Electron contamination
- MCNP
- Monte Carlo
- Virtual source

### ASJC Scopus subject areas

- Biophysics

### Cite this

*Medical Physics*,

*27*(1), 166-172. https://doi.org/10.1118/1.598881

**A virtual source model for Monte Carlo modeling of arbitrary intensity distributions.** / Chetty, I.; DeMarco, J. J.; Solberg, T. D.

Research output: Contribution to journal › Article

*Medical Physics*, vol. 27, no. 1, pp. 166-172. https://doi.org/10.1118/1.598881

}

TY - JOUR

T1 - A virtual source model for Monte Carlo modeling of arbitrary intensity distributions

AU - Chetty, I.

AU - DeMarco, J. J.

AU - Solberg, T. D.

PY - 2000/1

Y1 - 2000/1

N2 - A photon virtual source model was developed for simulating arbitrary, external beam, intensity distributions using the Monte Carlo method. The source model consists of a photon fluence grid composed of a matrix of square elements, located 25-cm downstream from the linear accelerator target. Each particle originating from the fluence map is characterized by the seven phase space parameters, position (x, y, z), direction (u, v, w), and energy. The map was reconstructed from fluence and energy spectra acquired by modeling components of the linear accelerator treatment head using the Monte Carlo code MCNP4B. The effect of contaminant electrons is accounted for by the use of a sub-source derived from a phase-space simulation of a 25-MV linac treatment head using the code BEAM. The BEAM sub-source was incorporated into the MCNP4B phase-space model and is sampled using a field-size dependent sampling ratio. A Gaussian blurring kernel is convolved with the photon fluence map to account for the finite focal spot size and scattering effects from structures such as the flattening filter and MLC leaves. Depth dose and profile source calculations for 6-MV and 25-MV photon beams, for 5 x 5 cm2, 10x 10 cm2, and 15x 15 cm2 field sizes, are in good agreement with measurement and are well within acceptability criteria suggested by the AAPM Task Group Report No. 53. Irregular field calculations compared with film measurement and with a 3-D pencil beam algorithm show that the source model is capable of accurately simulating arbitrary MLC fields.

AB - A photon virtual source model was developed for simulating arbitrary, external beam, intensity distributions using the Monte Carlo method. The source model consists of a photon fluence grid composed of a matrix of square elements, located 25-cm downstream from the linear accelerator target. Each particle originating from the fluence map is characterized by the seven phase space parameters, position (x, y, z), direction (u, v, w), and energy. The map was reconstructed from fluence and energy spectra acquired by modeling components of the linear accelerator treatment head using the Monte Carlo code MCNP4B. The effect of contaminant electrons is accounted for by the use of a sub-source derived from a phase-space simulation of a 25-MV linac treatment head using the code BEAM. The BEAM sub-source was incorporated into the MCNP4B phase-space model and is sampled using a field-size dependent sampling ratio. A Gaussian blurring kernel is convolved with the photon fluence map to account for the finite focal spot size and scattering effects from structures such as the flattening filter and MLC leaves. Depth dose and profile source calculations for 6-MV and 25-MV photon beams, for 5 x 5 cm2, 10x 10 cm2, and 15x 15 cm2 field sizes, are in good agreement with measurement and are well within acceptability criteria suggested by the AAPM Task Group Report No. 53. Irregular field calculations compared with film measurement and with a 3-D pencil beam algorithm show that the source model is capable of accurately simulating arbitrary MLC fields.

KW - Electron contamination

KW - MCNP

KW - Monte Carlo

KW - Virtual source

UR - http://www.scopus.com/inward/record.url?scp=0033965864&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0033965864&partnerID=8YFLogxK

U2 - 10.1118/1.598881

DO - 10.1118/1.598881

M3 - Article

C2 - 10659754

AN - SCOPUS:0033965864

VL - 27

SP - 166

EP - 172

JO - Medical Physics

JF - Medical Physics

SN - 0094-2405

IS - 1

ER -