Authors

Charles A Baron, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Jefferson Medical College
Musaddiq J Awan, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Department of Radiation Oncology, Case Western Reserve University
Abdallah S R Mohamed, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Department of Clinical Oncology, Faculty of Medicine, Alexandria University
Imad Akel, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; American University of Beirut Medical Center
David I Rosenthal, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center
G Brandon Gunn, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center
Adam S Garden, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center
Brandon A Dyer, Department of Radiation Medicine, Oregon Health and Science University
Laurence Court, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Graduate School of Biomedical Science, University of Texas Health Science Center
Parag R Sevak, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; University of Texas Medical Branch
Esengul Kocak-Uzel, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Department of Radiation Oncology, Sisli Etfal Teaching and Research Hospital
Clifton D Fuller, Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center; Department of Radiation Medicine, Oregon Health and Science University; Graduate School of Biomedical Science, University of Texas Health Science Center

Document Type

Article

Publication Date

1-8-2014

Comments

This article has been peer reviewed. It was published in: Journal of Applied Clinical Medical Physics.

Volume 16, Issue 1, 2015, Pages 159-169.

The published version is available at DOI: 10.1120/jacmp.v16i1.5108

Copyright © 2015 The Authors

Abstract

Larynx may alternatively serve as a target or organs at risk (OAR) in head and neck cancer (HNC) image-guided radiotherapy (IGRT). The objective of this study was to estimate IGRT parameters required for larynx positional error independent of isocentric alignment and suggest population-based compensatory margins. Ten HNC patients receiving radiotherapy (RT) with daily CT on-rails imaging were assessed. Seven landmark points were placed on each daily scan. Taking the most superior-anterior point of the C5 vertebra as a reference isocenter for each scan, residual displacement vectors to the other six points were calculated postisocentric alignment. Subsequently, using the first scan as a reference, the magnitude of vector differences for all six points for all scans over the course of treatment was calculated. Residual systematic and random error and the necessary compensatory CTV-to-PTV and OAR-to-PRV margins were calculated, using both observational cohort data and a bootstrap-resampled population estimator. The grand mean displacements for all anatomical points was 5.07 mm, with mean systematic error of 1.1 mm and mean random setup error of 2.63 mm, while bootstrapped POIs grand mean displacement was 5.09 mm, with mean systematic error of 1.23 mm and mean random setup error of 2.61 mm. Required margin for CTV-PTV expansion was 4.6 mm for all cohort points, while the bootstrap estimator of the equivalent margin was 4.9 mm. The calculated OAR-to-PRV expansion for the observed residual setup error was 2.7 mm and bootstrap estimated expansion of 2.9 mm. We conclude that the interfractional larynx setup error is a significant source of RT setup/delivery error in HNC, both when the larynx is considered as a CTV or OAR. We estimate the need for a uniform expansion of 5 mm to compensate for setup error if the larynx is a target, or 3 mm if the larynx is an OAR, when using a nonlaryngeal bony isocenter.

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