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Title: Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation

Abstract

Inter- and intra-leaf transmission and head scatter can play significant roles in intensity modulated radiation therapy (IMRT)-based treatment deliveries. In order to accurately calculate the dose in the IMRT planning process, it is therefore important that the detailed geometry of the multi-leaf collimator (MLC), in addition to other components in the accelerator treatment head, be accurately modeled. In this paper, we have used the Monte Carlo method (MC) to develop a comprehensive model of the Varian 120 leaf MLC and have compared it against measurements in homogeneous phantom geometries under different IMRT delivery circumstances. We have developed a geometry module within the DPM MC code to simulate the detailed MLC design and the collimating jaws. Tests consisting of leakage, leaf positioning and static MLC shapes were performed to verify the accuracy of transport within the MLC model. The calculations show agreement within 2% in the high dose region for both film and ion-chamber measurements for these static shapes. Clinical IMRT treatment plans for the breast [both segmental MLC (SMLC) and dynamic MLC (DMLC)], prostate (SMLC) and head and neck split fields (SMLC) were also calculated and compared with film measurements. Such a range of cases were chosen to investigate themore » accuracy of the model as a function of modulation in the beamlet pattern, beamlet width, and field size. The overall agreement is within 2%/2 mm of the film data for all IMRT beams except the head and neck split field, which showed differences up to 5% in the high dose regions. Various sources of uncertainties in these comparisons are discussed.« less

Authors:
; ; ; ; ;  [1];  [2];  [2]
  1. University of Michigan, Department of Radiation Oncology, Ann Arbor, Michigan 48109-0010 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20951056
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 2; Other Information: DOI: 10.1118/1.2428405; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ACCURACY; COLLIMATORS; DOSIMETRY; HEAD; IONIZATION CHAMBERS; MAMMARY GLANDS; MODULATION; MONTE CARLO METHOD; NECK; PHANTOMS; PLANNING; PROSTATE; RADIATION DOSES; RADIOTHERAPY; SIMULATION; VERIFICATION

Citation Formats

Tyagi, Neelam, Moran, Jean M., Litzenberg, Dale W., Bielajew, Alex F., Fraass, Benedick A., Chetty, Indrin J., University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan 48109-2104, and University of Michigan, Department of Radiation Oncology, Ann Arbor, Michigan 48109-0010. Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation. United States: N. p., 2007. Web. doi:10.1118/1.2428405.
Tyagi, Neelam, Moran, Jean M., Litzenberg, Dale W., Bielajew, Alex F., Fraass, Benedick A., Chetty, Indrin J., University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan 48109-2104, & University of Michigan, Department of Radiation Oncology, Ann Arbor, Michigan 48109-0010. Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation. United States. doi:10.1118/1.2428405.
Tyagi, Neelam, Moran, Jean M., Litzenberg, Dale W., Bielajew, Alex F., Fraass, Benedick A., Chetty, Indrin J., University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan 48109-2104, and University of Michigan, Department of Radiation Oncology, Ann Arbor, Michigan 48109-0010. Thu . "Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation". United States. doi:10.1118/1.2428405.
@article{osti_20951056,
title = {Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation},
author = {Tyagi, Neelam and Moran, Jean M. and Litzenberg, Dale W. and Bielajew, Alex F. and Fraass, Benedick A. and Chetty, Indrin J. and University of Michigan, Department of Nuclear Engineering and Radiological Sciences, Ann Arbor, Michigan 48109-2104 and University of Michigan, Department of Radiation Oncology, Ann Arbor, Michigan 48109-0010},
abstractNote = {Inter- and intra-leaf transmission and head scatter can play significant roles in intensity modulated radiation therapy (IMRT)-based treatment deliveries. In order to accurately calculate the dose in the IMRT planning process, it is therefore important that the detailed geometry of the multi-leaf collimator (MLC), in addition to other components in the accelerator treatment head, be accurately modeled. In this paper, we have used the Monte Carlo method (MC) to develop a comprehensive model of the Varian 120 leaf MLC and have compared it against measurements in homogeneous phantom geometries under different IMRT delivery circumstances. We have developed a geometry module within the DPM MC code to simulate the detailed MLC design and the collimating jaws. Tests consisting of leakage, leaf positioning and static MLC shapes were performed to verify the accuracy of transport within the MLC model. The calculations show agreement within 2% in the high dose region for both film and ion-chamber measurements for these static shapes. Clinical IMRT treatment plans for the breast [both segmental MLC (SMLC) and dynamic MLC (DMLC)], prostate (SMLC) and head and neck split fields (SMLC) were also calculated and compared with film measurements. Such a range of cases were chosen to investigate the accuracy of the model as a function of modulation in the beamlet pattern, beamlet width, and field size. The overall agreement is within 2%/2 mm of the film data for all IMRT beams except the head and neck split field, which showed differences up to 5% in the high dose regions. Various sources of uncertainties in these comparisons are discussed.},
doi = {10.1118/1.2428405},
journal = {Medical Physics},
number = 2,
volume = 34,
place = {United States},
year = {Thu Feb 15 00:00:00 EST 2007},
month = {Thu Feb 15 00:00:00 EST 2007}
}