Are Lateral Electronic Portal Images Adequate for Accurate On-Line Daily Targeting of the Prostate? Results of a Prospective Study

Lometti, Michael W.; Thurston, Damon; Aubin, Michele; Bock, Andrea; Verhey, Lynn; Lockhart, James M.; Bland, Roger; Pouliot, Jean; Roach, Mack

doi:10.1016/j.meddos.2007.04.006

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Volume 33, Issue 1 , Pages 22-29, Spring 2008

Are Lateral Electronic Portal Images Adequate for Accurate On-Line Daily Targeting of the Prostate? Results of a Prospective Study

Michael W. Lometti, M.S.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
- Physics and Astronomy Department, San Francisco State University, San Francisco, CA
- Reprint requests to: Michael W. Lometti, M.S., Box 1708, University of California San Francisco Comprehensive Cancer Center, 1600 Divisadero Street, San Francisco, CA 94143.
Damon Thurston, B.S.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
- Physics and Astronomy Department, San Francisco State University, San Francisco, CA
Michele Aubin, M.S.E.E.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
Andrea Bock, Ph.D.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
Lynn Verhey, Ph.D.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
James M. Lockhart, Ph.D.
- Physics and Astronomy Department, San Francisco State University, San Francisco, CA
Roger Bland, Ph.D.
- Physics and Astronomy Department, San Francisco State University, San Francisco, CA
Jean Pouliot, Ph.D.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA
Mack Roach III, Ph.D.
- Department of Radiation Oncology, University of California San Francisco Comprehensive Cancer Center, San Francisco, CA

Received 24 October 2006; accepted 10 April 2007. published online 22 November 2007.

Abstract

The purpose of this report was to evaluate the magnitude of the error that would be introduced if only a lateral (LAT) portal image, as opposed to a pair of orthogonal images, was used to verify and correct daily setup errors and organ motion in external beam radiation therapy (EBRT) of prostate cancer. The 3-dimensional (3D) coordinates of gold markers from 12 consecutive prostate patients were reconstructed using a pair of orthogonal images. The data were re-analyzed using only the LAT images. Couch moves from the 2-dimensional (2D)-only data were compared with the complete 3D data set. The 2D-only data provided couch moves that differed on average from the 3D data by 2.3 ± 3.0, 0.0 ± 0.0, and 0.8 ± 1.0 mm in the Lat, AP, and SI directions, respectively. Along AP and SI axes, the LAT image provided positional information similar to the orthogonal pair. The error along the LAT axis may be acceptable provided lateral margins are large enough. A LAT-only setup protocol reduces patient treatment times and increases patient throughput. In most circumstances, with exceptions such as morbidly obese patients, acquisition of only a LAT image for daily targeting of the prostate will provide adequate positional precision.

Key Words: Prostate cancer, Prostate motion, Radiopaque markers, Electronic portal images, Setup error