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Title: Comparison of Monte Carlo collimator transport methods for photon treatment planning in radiotherapy

Abstract

Purpose: The aim of this work was a Monte Carlo (MC) based investigation of the impact of different radiation transport methods in collimators of a linear accelerator on photon beam characteristics, dose distributions, and efficiency. Thereby it is investigated if it is possible to use different simplifications in the radiation transport for some clinical situations in order to save calculation time. Methods: Within the Swiss Monte Carlo Plan, a GUI-based framework for photon MC treatment planning, different MC methods are available for the radiation transport through the collimators [secondary jaws and multileaf collimator (MLC)]: EGSnrc (reference), VMC++, and Pin (an in-house developed MC code). Additional nonfull transport methods were implemented in order to provide different complexity levels for the MC simulation: Considering collimator attenuation only, considering Compton scatter only or just the firstCompton process, and considering the collimators as totally absorbing. Furthermore, either a simple or an exact geometry of the collimators can be selected for the absorbing or attenuation method. Phasespaces directly above and dose distributions in a water phantom are analyzed for academic and clinical treatment fields using 6 and 15 MV beams, including intensity modulated radiation therapy with dynamic MLC. Results: For all MC transport methods, differencesmore » in the radial mean energy and radial energy fluence are within 1% inside the geometric field. Below the collimators, the energy fluence is underestimated for nonfull MC transport methods ranging from 5% for Compton to 100% for Absorbing. Gamma analysis using EGSnrc calculated doses as reference shows that the percentage of voxels fulfilling a 1% /1 mm criterion is at least 98% when using VMC++, Compton, or firstCompton transport methods. When using the methods Pin, Transmission, Flat-Transmission, Flat-Absorbing or Absorbing, the mean value of points fulfilling this criterion over all tested cases is 97%, 88%, 74%, 68%, or 65%, respectively. However, compared to EGSnrc calculations, the gain in efficiency is a factor of up to 10 for VMC++ and up to 48 for the absorbing method. Conclusions: The results of this investigation suggest that it is an option to use a simple transport technique in the initial treatment planning process and use more accurate transport methods for the final dose calculation accepting longer calculation times.« less

Authors:
; ; ; ;  [1]
  1. Division of Medical Radiation Physics, Inselspital, Berne University Hospital, and University of Berne, CH-3010 Berne (Switzerland)
Publication Date:
OSTI Identifier:
22096620
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 37; Journal Issue: 2; Other Information: (c) 2010 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; COLLIMATORS; EFFICIENCY; LINEAR ACCELERATORS; MONTE CARLO METHOD; PHANTOMS; PHOTON BEAMS; PHOTONS; PLANNING; RADIATION DOSE DISTRIBUTIONS; RADIATION DOSES; RADIATION TRANSPORT; RADIOTHERAPY; SIMULATION

Citation Formats

Schmidhalter, D., Manser, P., Frei, D., Volken, W., and Fix, M. K. Comparison of Monte Carlo collimator transport methods for photon treatment planning in radiotherapy. United States: N. p., 2010. Web. doi:10.1118/1.3284978.
Schmidhalter, D., Manser, P., Frei, D., Volken, W., & Fix, M. K. Comparison of Monte Carlo collimator transport methods for photon treatment planning in radiotherapy. United States. https://doi.org/10.1118/1.3284978
Schmidhalter, D., Manser, P., Frei, D., Volken, W., and Fix, M. K. 2010. "Comparison of Monte Carlo collimator transport methods for photon treatment planning in radiotherapy". United States. https://doi.org/10.1118/1.3284978.
@article{osti_22096620,
title = {Comparison of Monte Carlo collimator transport methods for photon treatment planning in radiotherapy},
author = {Schmidhalter, D. and Manser, P. and Frei, D. and Volken, W. and Fix, M. K.},
abstractNote = {Purpose: The aim of this work was a Monte Carlo (MC) based investigation of the impact of different radiation transport methods in collimators of a linear accelerator on photon beam characteristics, dose distributions, and efficiency. Thereby it is investigated if it is possible to use different simplifications in the radiation transport for some clinical situations in order to save calculation time. Methods: Within the Swiss Monte Carlo Plan, a GUI-based framework for photon MC treatment planning, different MC methods are available for the radiation transport through the collimators [secondary jaws and multileaf collimator (MLC)]: EGSnrc (reference), VMC++, and Pin (an in-house developed MC code). Additional nonfull transport methods were implemented in order to provide different complexity levels for the MC simulation: Considering collimator attenuation only, considering Compton scatter only or just the firstCompton process, and considering the collimators as totally absorbing. Furthermore, either a simple or an exact geometry of the collimators can be selected for the absorbing or attenuation method. Phasespaces directly above and dose distributions in a water phantom are analyzed for academic and clinical treatment fields using 6 and 15 MV beams, including intensity modulated radiation therapy with dynamic MLC. Results: For all MC transport methods, differences in the radial mean energy and radial energy fluence are within 1% inside the geometric field. Below the collimators, the energy fluence is underestimated for nonfull MC transport methods ranging from 5% for Compton to 100% for Absorbing. Gamma analysis using EGSnrc calculated doses as reference shows that the percentage of voxels fulfilling a 1% /1 mm criterion is at least 98% when using VMC++, Compton, or firstCompton transport methods. When using the methods Pin, Transmission, Flat-Transmission, Flat-Absorbing or Absorbing, the mean value of points fulfilling this criterion over all tested cases is 97%, 88%, 74%, 68%, or 65%, respectively. However, compared to EGSnrc calculations, the gain in efficiency is a factor of up to 10 for VMC++ and up to 48 for the absorbing method. Conclusions: The results of this investigation suggest that it is an option to use a simple transport technique in the initial treatment planning process and use more accurate transport methods for the final dose calculation accepting longer calculation times.},
doi = {10.1118/1.3284978},
url = {https://www.osti.gov/biblio/22096620}, journal = {Medical Physics},
issn = {0094-2405},
number = 2,
volume = 37,
place = {United States},
year = {Mon Feb 15 00:00:00 EST 2010},
month = {Mon Feb 15 00:00:00 EST 2010}
}