Photon beam characterization and modelling for Monte Carlo treatment planning.

Photon beams of 4, 6 and 15 MV from Varian Clinac 2100C and 2300C/D accelerators were simulated using the EGS4/BEAM code system. The accelerators were modelled as a combination of component modules (CMs) consisting of a target, primary collimator, exit window, flattening filter, monitor chamber, secondary collimator, ring collimator, photon jaws and protection window. A full phase space file was scored directly above the upper photon jaws and analysed using beam data processing software, BEAMDP, to derive the beam characteristics, such as planar fluence, angular distribution, energy spectrum and the fractional contributions of each individual CM. A multiple-source model has been further developed to reconstruct the original phase space. Separate sources were created with accurate source intensity, energy, fluence and angular distributions for the target, primary collimator and flattening filter. Good agreement (within 2%) between the Monte Carlo calculations with the source model and those with the original phase space was achieved in the dose distributions for field sizes of 4 cm x 4 cm to 40 cm x 40 cm at source surface distances (SSDs) of 80-120 cm. The dose distributions in lung and bone heterogeneous phantoms have also been found to be in good agreement (within 2%) for 4, 6 and 15 MV photon beams for various field sizes between the Monte Carlo calculations with the source model and those with the original phase space.

[1]  C. Ma,et al.  Monte Carlo calculations of electron beam output factors for a medical linear accelerator. , 1998, Physics in medicine and biology.

[2]  F. H. Attix,et al.  5 – Monte Carlo Techniques of Electron and Photon Transport for Radiation Dosimetry , 1990 .

[3]  K R Shortt,et al.  Electron beam dose distributions near standard inhomogeneities , 1986 .

[4]  David W. O. Rogers,et al.  Presta: The parameter reduced electron-step transport algorithm for electron monte carlo transport , 1986 .

[5]  A Ahnesjö,et al.  Analytic modeling of photon scatter from flattening filters in photon therapy beams. , 1994, Medical physics.

[6]  C. Ma,et al.  Accurate characterization of Monte Carlo calculated electron beams for radiotherapy , 1997 .

[7]  Pedro Andreo,et al.  Stopping-power ratios and their uncertainties for clinical electron beam dosimetry , 1989 .

[8]  T. Mackie 6 – Applications of the Monte Carlo Method in Radiotherapy , 1990 .

[9]  T Knöös,et al.  Application of the convolution method for calculation of output factors for therapy photon beams. , 1992, Medical physics.

[10]  T. Mackie,et al.  A dual source photon beam model used in convolution/superposition dose calculations for clinical megavoltage x-ray beams. , 1997, Medical physics.

[11]  R Mohan,et al.  Energy and angular distributions of photons from medical linear accelerators. , 1985, Medical physics.

[12]  C. Ma,et al.  Stopping-power ratios for clinical electron beams from a scatter-foil linear accelerator. , 1999, Physics in medicine and biology.

[13]  Christine L. Hartmann-Siantar,et al.  Lawrence Livermore National Laboratory`s PEREGRINE project , 1997 .

[14]  J J DeMarco,et al.  A CT-based Monte Carlo simulation tool for dosimetry planning and analysis. , 1998, Medical physics.

[15]  A Ahnesjö,et al.  Collimator scatter in photon therapy beams. , 1995, Medical physics.

[16]  C. Ma,et al.  Clinical implementation of a Monte Carlo treatment planning system. , 1999, Medical physics.

[17]  S. C. Prasad,et al.  Clinical electron-beam dosimetry: report of AAPM Radiation Therapy Committee Task Group No. 25. , 1991, Medical physics.

[18]  R Mohan,et al.  A Monte Carlo model of photon beams used in radiation therapy. , 1995, Medical physics.

[19]  P. Andreo Monte Carlo techniques in medical radiation physics. , 1991, Physics in medicine and biology.

[20]  T R Mackie,et al.  Calculating output factors for photon beam radiotherapy using a convolution/superposition method based on a dual source photon beam model. , 1997, Medical physics.

[21]  E L Chaney,et al.  A Monte Carlo study of accelerator head scatter. , 1994, Medical physics.

[22]  T. Mackie,et al.  Calculating dose and output factors for wedged photon radiotherapy fields using a convolution/superposition method. , 1997, Medical physics.

[23]  Udale-Smith Ma,et al.  A Monte Carlo investigation of high energy electron beams used in radiotherapy. , 1990 .

[24]  Chang-ming Ma,et al.  Characterization of computer simulated radiotherapy beams for Monte-Carlo treatment planning , 1998 .

[25]  C. Ma,et al.  BEAM: a Monte Carlo code to simulate radiotherapy treatment units. , 1995, Medical physics.

[26]  A L Boyer,et al.  An analytic calculation of the energy fluence spectrum of a linear accelerator. , 1994, Medical physics.

[27]  S B Jiang,et al.  Monte Carlo modelling of electron beams from medical accelerators. , 1999, Physics in medicine and biology.