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Title: An anatomically realistic lung model for Monte Carlo-based dose calculations

Abstract

Treatment planning for disease sites with large variations of electron density in neighboring tissues requires an accurate description of the geometry. This self-evident statement is especially true for the lung, a highly complex organ having structures with a wide range of sizes that range from about 10{sup -4} to 1 cm. In treatment planning, the lung is commonly modeled by a voxelized geometry obtained using computed tomography (CT) data at various resolutions. The simplest such model, which is often used for QA and validation work, is the atomic mix or mean density model, in which the entire lung is homogenized and given a mean (volume-averaged) density. The purpose of this paper is (i) to describe a new heterogeneous random lung model, which is based on morphological data of the human lung, and (ii) use this model to assess the differences in dose calculations between an actual lung (as represented by our model) and a mean density (homogenized) lung. Eventually, we plan to use the random lung model to assess the accuracy of CT-based treatment plans of the lung. For this paper, we have used Monte Carlo methods to make accurate comparisons between dose calculations for the random lung model andmore » the mean density model. For four realizations of the random lung model, we used a single photon beam, with two different energies (6 and 18 MV) and four field sizes (1x1, 5x5, 10x10, and 20x20 cm{sup 2}). We found a maximum difference of 34% of D{sub max} with the 1x1, 18 MV beam along the central axis (CAX). A ''shadow'' region distal to the lung, with dose reduction up to 7% of D{sub max}, exists for the same realization. The dose perturbations decrease for larger field sizes, but the magnitude of the differences in the shadow region is nearly independent of the field size. We also observe that, compared to the mean density model, the random structures inside the heterogeneous lung can alter the shape of the isodose lines, leading to a broadening or shrinking of the penumbra region. For small field sizes, the mean lung doses significantly depend on the structures' relative locations to the beam. In addition to these comparisons between the random lung and mean density models, we also provide a preliminary comparison between dose calculations for the random lung model and a voxelized version of this model at 0.4x0.4x0.4 cm{sup 3} resolution. Overall, this study is relevant to treatment planning for lung tumors, especially in situations where small field sizes are used. Our results show that for such situations, the mean density model of the lung is inadequate, and a more accurate CT model of the lung is required. Future work with our model will involve patient motion, setup errors, and recommendations for the resolution of CT models.« less

Authors:
; ;  [1];  [2]
  1. Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20951091
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 34; Journal Issue: 3; Other Information: DOI: 10.1118/1.2437284; (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; COMPUTERIZED TOMOGRAPHY; DOSIMETRY; ELECTRON DENSITY; ERRORS; LUNGS; MONTE CARLO METHOD; NEOPLASMS; PATIENTS; PHOTON BEAMS; PLANNING; RADIATION DOSES; RECOMMENDATIONS; SPATIAL RESOLUTION; VALIDATION

Citation Formats

Liang Liang, Larsen, Edward W., Chetty, Indrin J., and Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska 68198-7521. An anatomically realistic lung model for Monte Carlo-based dose calculations. United States: N. p., 2007. Web. doi:10.1118/1.2437284.
Liang Liang, Larsen, Edward W., Chetty, Indrin J., & Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska 68198-7521. An anatomically realistic lung model for Monte Carlo-based dose calculations. United States. doi:10.1118/1.2437284.
Liang Liang, Larsen, Edward W., Chetty, Indrin J., and Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska 68198-7521. Thu . "An anatomically realistic lung model for Monte Carlo-based dose calculations". United States. doi:10.1118/1.2437284.
@article{osti_20951091,
title = {An anatomically realistic lung model for Monte Carlo-based dose calculations},
author = {Liang Liang and Larsen, Edward W. and Chetty, Indrin J. and Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, Nebraska 68198-7521},
abstractNote = {Treatment planning for disease sites with large variations of electron density in neighboring tissues requires an accurate description of the geometry. This self-evident statement is especially true for the lung, a highly complex organ having structures with a wide range of sizes that range from about 10{sup -4} to 1 cm. In treatment planning, the lung is commonly modeled by a voxelized geometry obtained using computed tomography (CT) data at various resolutions. The simplest such model, which is often used for QA and validation work, is the atomic mix or mean density model, in which the entire lung is homogenized and given a mean (volume-averaged) density. The purpose of this paper is (i) to describe a new heterogeneous random lung model, which is based on morphological data of the human lung, and (ii) use this model to assess the differences in dose calculations between an actual lung (as represented by our model) and a mean density (homogenized) lung. Eventually, we plan to use the random lung model to assess the accuracy of CT-based treatment plans of the lung. For this paper, we have used Monte Carlo methods to make accurate comparisons between dose calculations for the random lung model and the mean density model. For four realizations of the random lung model, we used a single photon beam, with two different energies (6 and 18 MV) and four field sizes (1x1, 5x5, 10x10, and 20x20 cm{sup 2}). We found a maximum difference of 34% of D{sub max} with the 1x1, 18 MV beam along the central axis (CAX). A ''shadow'' region distal to the lung, with dose reduction up to 7% of D{sub max}, exists for the same realization. The dose perturbations decrease for larger field sizes, but the magnitude of the differences in the shadow region is nearly independent of the field size. We also observe that, compared to the mean density model, the random structures inside the heterogeneous lung can alter the shape of the isodose lines, leading to a broadening or shrinking of the penumbra region. For small field sizes, the mean lung doses significantly depend on the structures' relative locations to the beam. In addition to these comparisons between the random lung and mean density models, we also provide a preliminary comparison between dose calculations for the random lung model and a voxelized version of this model at 0.4x0.4x0.4 cm{sup 3} resolution. Overall, this study is relevant to treatment planning for lung tumors, especially in situations where small field sizes are used. Our results show that for such situations, the mean density model of the lung is inadequate, and a more accurate CT model of the lung is required. Future work with our model will involve patient motion, setup errors, and recommendations for the resolution of CT models.},
doi = {10.1118/1.2437284},
journal = {Medical Physics},
number = 3,
volume = 34,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}