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. J Appl Clin Med Phys 2014 Jan 08;16(1):5108
Date
02/14/2015Pubmed ID
25679151Pubmed Central ID
PMC5016194DOI
10.1120/jacmp.v16i1.5108Scopus ID
2-s2.0-84922895104 (requires institutional sign-in at Scopus site) 16 CitationsAbstract
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.
Author List
Baron CA, Awan MJ, Mohamed AS, Akel I, Rosenthal DI, Gunn GB, Garden AS, Dyer BA, Court L, Sevak PR, Kocak-Uzel E, Fuller CDAuthor
Musaddiq J. Awan MD Assistant Professor in the Radiation Oncology department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Head and Neck NeoplasmsHumans
Laryngeal Neoplasms
Organs at Risk
Quality Assurance, Health Care
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted
Radiotherapy Setup Errors
Radiotherapy, Intensity-Modulated
Tomography, X-Ray Computed
Tumor Burden