Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations

Scott E. Davidson, Jing Cui, Stephen Kry, Joseph O. Deasy, Geoffrey S. Ibbott, Milos Vicic, R. Allen White, David S. Followill

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Results: Dose calculations of the depth dose and profiles for field sizes 4×4 to 40×40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.

Original languageEnglish (US)
Pages (from-to)4842-4853
Number of pages12
JournalMedical Physics
Volume43
Issue number8
DOIs
StatePublished - Aug 1 2016

Fingerprint

Particle Accelerators
Radiotherapy
Monte Carlo Method
Linear Models
Clinical Trials
Electrons
Hospital Distribution Systems
Benchmarking
National Cancer Institute (U.S.)
Therapeutics

Keywords

  • clinical trial
  • Monte Carlo
  • source model

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging

Cite this

Davidson, S. E., Cui, J., Kry, S., Deasy, J. O., Ibbott, G. S., Vicic, M., ... Followill, D. S. (2016). Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations. Medical Physics, 43(8), 4842-4853. https://doi.org/10.1118/1.4955434

Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations. / Davidson, Scott E.; Cui, Jing; Kry, Stephen; Deasy, Joseph O.; Ibbott, Geoffrey S.; Vicic, Milos; White, R. Allen; Followill, David S.

In: Medical Physics, Vol. 43, No. 8, 01.08.2016, p. 4842-4853.

Research output: Contribution to journalArticle

Davidson, SE, Cui, J, Kry, S, Deasy, JO, Ibbott, GS, Vicic, M, White, RA & Followill, DS 2016, 'Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations', Medical Physics, vol. 43, no. 8, pp. 4842-4853. https://doi.org/10.1118/1.4955434
Davidson, Scott E. ; Cui, Jing ; Kry, Stephen ; Deasy, Joseph O. ; Ibbott, Geoffrey S. ; Vicic, Milos ; White, R. Allen ; Followill, David S. / Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations. In: Medical Physics. 2016 ; Vol. 43, No. 8. pp. 4842-4853.
@article{581fe6a267fe4e54bc99106c174deb0a,
title = "Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations",
abstract = "Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Results: Dose calculations of the depth dose and profiles for field sizes 4×4 to 40×40 cm agree with measurement within 2{\%} of the maximum dose or 2 mm distance to agreement (DTA) for 95{\%} of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3{\%} in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3{\%} of maximum dose and 2 mm DTA was applied with a pass rate of least 85{\%} in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.",
keywords = "clinical trial, Monte Carlo, source model",
author = "Davidson, {Scott E.} and Jing Cui and Stephen Kry and Deasy, {Joseph O.} and Ibbott, {Geoffrey S.} and Milos Vicic and White, {R. Allen} and Followill, {David S.}",
year = "2016",
month = "8",
day = "1",
doi = "10.1118/1.4955434",
language = "English (US)",
volume = "43",
pages = "4842--4853",
journal = "Medical Physics",
issn = "0094-2405",
publisher = "AAPM - American Association of Physicists in Medicine",
number = "8",

}

TY - JOUR

T1 - Modification and validation of an analytical source model for external beam radiotherapy Monte Carlo dose calculations

AU - Davidson, Scott E.

AU - Cui, Jing

AU - Kry, Stephen

AU - Deasy, Joseph O.

AU - Ibbott, Geoffrey S.

AU - Vicic, Milos

AU - White, R. Allen

AU - Followill, David S.

PY - 2016/8/1

Y1 - 2016/8/1

N2 - Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Results: Dose calculations of the depth dose and profiles for field sizes 4×4 to 40×40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.

AB - Purpose: A dose calculation tool, which combines the accuracy of the dose planning method (DPM) Monte Carlo code and the versatility of a practical analytical multisource model, which was previously reported has been improved and validated for the Varian 6 and 10 MV linear accelerators (linacs). The calculation tool can be used to calculate doses in advanced clinical application studies. One shortcoming of current clinical trials that report dose from patient plans is the lack of a standardized dose calculation methodology. Because commercial treatment planning systems (TPSs) have their own dose calculation algorithms and the clinical trial participant who uses these systems is responsible for commissioning the beam model, variation exists in the reported calculated dose distributions. Today's modern linac is manufactured to tight specifications so that variability within a linac model is quite low. The expectation is that a single dose calculation tool for a specific linac model can be used to accurately recalculate dose from patient plans that have been submitted to the clinical trial community from any institution. The calculation tool would provide for a more meaningful outcome analysis. Methods: The analytical source model was described by a primary point source, a secondary extra-focal source, and a contaminant electron source. Off-axis energy softening and fluence effects were also included. The additions of hyperbolic functions have been incorporated into the model to correct for the changes in output and in electron contamination with field size. A multileaf collimator (MLC) model is included to facilitate phantom and patient dose calculations. An offset to the MLC leaf positions was used to correct for the rudimentary assumed primary point source. Results: Dose calculations of the depth dose and profiles for field sizes 4×4 to 40×40 cm agree with measurement within 2% of the maximum dose or 2 mm distance to agreement (DTA) for 95% of the data points tested. The model was capable of predicting the depth of the maximum dose within 1 mm. Anthropomorphic phantom benchmark testing of modulated and patterned MLCs treatment plans showed agreement to measurement within 3% in target regions using thermoluminescent dosimeters (TLD). Using radiochromic film normalized to TLD, a gamma criteria of 3% of maximum dose and 2 mm DTA was applied with a pass rate of least 85% in the high dose, high gradient, and low dose regions. Finally, recalculations of patient plans using DPM showed good agreement relative to a commercial TPS when comparing dose volume histograms and 2D dose distributions. Conclusions: A unique analytical source model coupled to the dose planning method Monte Carlo dose calculation code has been modified and validated using basic beam data and anthropomorphic phantom measurement. While this tool can be applied in general use for a particular linac model, specifically it was developed to provide a singular methodology to independently assess treatment plan dose distributions from those clinical institutions participating in National Cancer Institute trials.

KW - clinical trial

KW - Monte Carlo

KW - source model

UR - http://www.scopus.com/inward/record.url?scp=84979979838&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84979979838&partnerID=8YFLogxK

U2 - 10.1118/1.4955434

DO - 10.1118/1.4955434

M3 - Article

C2 - 27487902

AN - SCOPUS:84979979838

VL - 43

SP - 4842

EP - 4853

JO - Medical Physics

JF - Medical Physics

SN - 0094-2405

IS - 8

ER -