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Title: Realistic respiratory motion margins for external beam partial breast irradiation

Abstract

Purpose: Respiratory margins for partial breast irradiation (PBI) have been largely based on geometric observations, which may overestimate the margin required for dosimetric coverage. In this study, dosimetric population-based respiratory margins and margin formulas for external beam partial breast irradiation are determined. Methods: Volunteer respiratory data and anterior–posterior (AP) dose profiles from clinical treatment plans of 28 3D conformal radiotherapy (3DCRT) PBI patient plans were used to determine population-based respiratory margins. The peak-to-peak amplitudes (A) of realistic respiratory motion data from healthy volunteers were scaled from A = 1 to 10 mm to create respiratory motion probability density functions. Dose profiles were convolved with the respiratory probability density functions to produce blurred dose profiles accounting for respiratory motion. The required margins were found by measuring the distance between the simulated treatment and original dose profiles at the 95% isodose level. Results: The symmetric dosimetric respiratory margins to cover 90%, 95%, and 100% of the simulated treatment population were 1.5, 2, and 4 mm, respectively. With patient set up at end exhale, the required margins were larger in the anterior direction than the posterior. For respiratory amplitudes less than 5 mm, the population-based margins can be expressed as a fraction ofmore » the extent of respiratory motion. The derived formulas in the anterior/posterior directions for 90%, 95%, and 100% simulated population coverage were 0.45A/0.25A, 0.50A/0.30A, and 0.70A/0.40A. The differences in formulas for different population coverage criteria demonstrate that respiratory trace shape and baseline drift characteristics affect individual respiratory margins even for the same average peak-to-peak amplitude. Conclusions: A methodology for determining population-based respiratory margins using real respiratory motion patterns and dose profiles in the AP direction was described. It was found that the currently used respiratory margin of 5 mm in partial breast irradiation may be overly conservative for many 3DCRT PBI patients. Amplitude alone was found to be insufficient to determine patient-specific margins: individual respiratory trace shape and baseline drift both contributed to the dosimetric target coverage. With respiratory coaching, individualized respiratory margins smaller than the full extent of motion could reduce planning target volumes while ensuring adequate coverage under respiratory motion.« less

Authors:
;  [1];  [2];  [1];  [2];  [2]
  1. Department of Medical Physics, Tom Baker Cancer Centre, Calgary, Alberta T2N 4N2 (Canada)
  2. (Canada)
Publication Date:
OSTI Identifier:
22581367
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 9; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; AMPLITUDES; BEAMS; IRRADIATION; MAMMARY GLANDS; PATIENTS; PROBABILITY DENSITY FUNCTIONS; RADIATION DOSES; RADIOTHERAPY; SIMULATION

Citation Formats

Conroy, Leigh, Quirk, Sarah, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Smith, Wendy L., E-mail: wendy.smith@albertahealthservices.ca, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, and Department of Oncology, University of Calgary, Calgary, Alberta T2N 1N4. Realistic respiratory motion margins for external beam partial breast irradiation. United States: N. p., 2015. Web. doi:10.1118/1.4928141.
Conroy, Leigh, Quirk, Sarah, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Smith, Wendy L., E-mail: wendy.smith@albertahealthservices.ca, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, & Department of Oncology, University of Calgary, Calgary, Alberta T2N 1N4. Realistic respiratory motion margins for external beam partial breast irradiation. United States. doi:10.1118/1.4928141.
Conroy, Leigh, Quirk, Sarah, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, Smith, Wendy L., E-mail: wendy.smith@albertahealthservices.ca, Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4, and Department of Oncology, University of Calgary, Calgary, Alberta T2N 1N4. Tue . "Realistic respiratory motion margins for external beam partial breast irradiation". United States. doi:10.1118/1.4928141.
@article{osti_22581367,
title = {Realistic respiratory motion margins for external beam partial breast irradiation},
author = {Conroy, Leigh and Quirk, Sarah and Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4 and Smith, Wendy L., E-mail: wendy.smith@albertahealthservices.ca and Department of Physics and Astronomy, University of Calgary, Calgary, Alberta T2N 1N4 and Department of Oncology, University of Calgary, Calgary, Alberta T2N 1N4},
abstractNote = {Purpose: Respiratory margins for partial breast irradiation (PBI) have been largely based on geometric observations, which may overestimate the margin required for dosimetric coverage. In this study, dosimetric population-based respiratory margins and margin formulas for external beam partial breast irradiation are determined. Methods: Volunteer respiratory data and anterior–posterior (AP) dose profiles from clinical treatment plans of 28 3D conformal radiotherapy (3DCRT) PBI patient plans were used to determine population-based respiratory margins. The peak-to-peak amplitudes (A) of realistic respiratory motion data from healthy volunteers were scaled from A = 1 to 10 mm to create respiratory motion probability density functions. Dose profiles were convolved with the respiratory probability density functions to produce blurred dose profiles accounting for respiratory motion. The required margins were found by measuring the distance between the simulated treatment and original dose profiles at the 95% isodose level. Results: The symmetric dosimetric respiratory margins to cover 90%, 95%, and 100% of the simulated treatment population were 1.5, 2, and 4 mm, respectively. With patient set up at end exhale, the required margins were larger in the anterior direction than the posterior. For respiratory amplitudes less than 5 mm, the population-based margins can be expressed as a fraction of the extent of respiratory motion. The derived formulas in the anterior/posterior directions for 90%, 95%, and 100% simulated population coverage were 0.45A/0.25A, 0.50A/0.30A, and 0.70A/0.40A. The differences in formulas for different population coverage criteria demonstrate that respiratory trace shape and baseline drift characteristics affect individual respiratory margins even for the same average peak-to-peak amplitude. Conclusions: A methodology for determining population-based respiratory margins using real respiratory motion patterns and dose profiles in the AP direction was described. It was found that the currently used respiratory margin of 5 mm in partial breast irradiation may be overly conservative for many 3DCRT PBI patients. Amplitude alone was found to be insufficient to determine patient-specific margins: individual respiratory trace shape and baseline drift both contributed to the dosimetric target coverage. With respiratory coaching, individualized respiratory margins smaller than the full extent of motion could reduce planning target volumes while ensuring adequate coverage under respiratory motion.},
doi = {10.1118/1.4928141},
journal = {Medical Physics},
number = 9,
volume = 42,
place = {United States},
year = {Tue Sep 15 00:00:00 EDT 2015},
month = {Tue Sep 15 00:00:00 EDT 2015}
}