Comparison of Spine, Carina, and Tumor as Registration Landmarks for Volumetric Image-Guided Lung Radiotherapy
Received 8 April 2008; received in revised form 27 June 2008; accepted 29 June 2008. published online 18 September 2008.
Purpose
To assess the feasibility, reproducibility, and accuracy of volumetric lung image guidance using different thoracic landmarks for image registration.
Methods and Materials
In 30 lung patients, four independent observers conducted automated and manual image registrations on Day 1 cone-beam computed tomography data sets using the spine, carina, and tumor (720 image registrations). The image registration was timed, and the couch displacements were recorded. The intraclass correlation was used to assess reproducibility, and the Bland-Altman analysis was used to compare the automatic and manual matching methods. Tumor coverage (accuracy) was assessed through grading the tumor position after image matching against the internal target volume and planning target volume.
Results
The image-guided process took an average of 1 min for all techniques, with the exception of manual tumor matching, which took 4 min. Reproducibility was greatest for automatic carina matching (intraclass correlation, 0.90–0.93) and lowest for manual tumor matching (intraclass correlation, 0.07–0.43) in the left-right, superoinferior, and anteroposterior directions, respectively. The Bland-Altman analysis showed no significant difference between the automatic and manual registration methods. The tumor was within the internal target volume 62% and 60% of the time and was outside the internal target volume, but within the planning target volume, 38% and 40% of the time after automatic spine and automatic carina matching, respectively.
Conclusion
For advanced lung cancer, the spine or carina can be used equally for cone-beam computed tomography image registration without compromising target coverage. The carina was more reproducible than the spine, but additional analysis is required to confirm its validation as a tumor surrogate. Soft-tissue registration is unsuitable at present, given the limitations in contrast resolution and the high interobserver variability.
‡St. James Institute of Oncology, Leeds Teaching Hospitals, National Health Service Trust, Leeds, England
Reprint requests to: Jane Higgins, B.Sc., Cobalt Lounge, 2B, Princess Margaret Hospital, 610 University Ave., Toronto, ON M5G 2M9 Canada. Tel: (416) 946-4501, ext. 4949; Fax: (416) 946-2019
Supported in part by Elekta Inc., B. Research Grant, and the McNaughton Fund for Thoracic Radiation Oncology, Princess Margaret Hospital Foundation.
Presented in part at the 49th Annual Meeting of the American Society for Therapeutic Radiology and Oncology, Los Angeles, CA, October 28 to November 1, 2007.
Conflict of interest: Potential, supported by Elekta, Inc.
ABSTRACT