Title

Estimation of daily interfractional larynx residual setup error after isocentric alignment for head and neck radiotherapy: quality assurance implications for target volume and organs-at-risk margination using daily CT on- rails imaging.

Authors

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

Document Type

Article

Publication Date

1-1-2015

Comments

This article has been peer reviewed. It was published in: Journal of applied clinical medical physics.

Volume 16, Issue 1, 2015, Page 5108.

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.