# Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space

## Abstract

We present a method for condensing the photon energy and angular distributions obtained from Monte Carlo simulations of medical accelerators. This method represents the output as a series of correlated histograms and as such is well-suited for inclusion as the photon-source package for Monte Carlo codes used to determine the dose distributions in photon teletherapy. The method accounts for the isocenter-plane variations of the photon energy spectral distributions with increasing distance from the beam central axis for radiation produced in the bremsstrahlung target as well as for radiation scattered by the various treatment machine components within the accelerator head. Comparison of the isocenter energy fluence computed by this algorithm with that of the underlying full-physics Monte Carlo photon phase space indicates that energy fluence errors are less than 1{percent} of the maximum energy fluence for a range of open-field sizes. Comparison of jaw-edge penumbrae shows that the angular distributions of the photons are accurately reproduced. The Monte Carlo sampling efficiency (the fraction of generated photons which clear the collimator jaws) of the algorithm is approximately 83{percent} for an open 10{times}10 field, rising to approximately 96{percent} for an open 40{times}40 field. Data file sizes for a typical medical accelerator, at amore »

- Authors:

- Lawrence Livermore National Laboratory, Livermore, California 94550 (United States)
- Medical College of Virginia/Virginia Commonwealth University, Richmond, Virginia 23298 (United States)

- Publication Date:

- OSTI Identifier:
- 351855

- Resource Type:
- Journal Article

- Journal Name:
- Medical Physics

- Additional Journal Information:
- Journal Volume: 26; Journal Issue: 7; Other Information: PBD: Jul 1999

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 55 BIOLOGY AND MEDICINE, BASIC STUDIES; DOSIMETRY; BREMSSTRAHLUNG; MONTE CARLO METHOD; RADIOTHERAPY; ACCELERATORS; PHASE SPACE; RADIATION DOSES; PHOTON BEAMS; ANGULAR DISTRIBUTION; ALGORITHMS; COLLIMATORS

### Citation Formats

```
Schach von Wittenau, A.E., Cox, L.J., Bergstrom, P.M. Jr., Chandler, W.P., Siantar, C.L., and Mohan, R.
```*Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space*. United States: N. p., 1999.
Web. doi:10.1118/1.598613.

```
Schach von Wittenau, A.E., Cox, L.J., Bergstrom, P.M. Jr., Chandler, W.P., Siantar, C.L., & Mohan, R.
```*Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space*. United States. doi:10.1118/1.598613.

```
Schach von Wittenau, A.E., Cox, L.J., Bergstrom, P.M. Jr., Chandler, W.P., Siantar, C.L., and Mohan, R. Thu .
"Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space". United States. doi:10.1118/1.598613.
```

```
@article{osti_351855,
```

title = {Correlated histogram representation of Monte Carlo derived medical accelerator photon-output phase space},

author = {Schach von Wittenau, A.E. and Cox, L.J. and Bergstrom, P.M. Jr. and Chandler, W.P. and Siantar, C.L. and Mohan, R.},

abstractNote = {We present a method for condensing the photon energy and angular distributions obtained from Monte Carlo simulations of medical accelerators. This method represents the output as a series of correlated histograms and as such is well-suited for inclusion as the photon-source package for Monte Carlo codes used to determine the dose distributions in photon teletherapy. The method accounts for the isocenter-plane variations of the photon energy spectral distributions with increasing distance from the beam central axis for radiation produced in the bremsstrahlung target as well as for radiation scattered by the various treatment machine components within the accelerator head. Comparison of the isocenter energy fluence computed by this algorithm with that of the underlying full-physics Monte Carlo photon phase space indicates that energy fluence errors are less than 1{percent} of the maximum energy fluence for a range of open-field sizes. Comparison of jaw-edge penumbrae shows that the angular distributions of the photons are accurately reproduced. The Monte Carlo sampling efficiency (the fraction of generated photons which clear the collimator jaws) of the algorithm is approximately 83{percent} for an open 10{times}10 field, rising to approximately 96{percent} for an open 40{times}40 field. Data file sizes for a typical medical accelerator, at a given energy, are approximately 150 kB, compared to the 1 GB size of the underlying full-physics phase space file. {copyright} {ital 1999 American Association of Physicists in Medicine.}},

doi = {10.1118/1.598613},

journal = {Medical Physics},

number = 7,

volume = 26,

place = {United States},

year = {1999},

month = {7}

}