title: Improved human observer performance in digital reconstructed radiograph verification in head and neck cancer radiotherapy.
abstract: OBJECTIVE
  Digitally reconstructed radiographs (DRRs) are routinely used as an a priori reference for setup correction in radiotherapy. The spatial resolution of DRRs may be improved to reduce setup error in fractionated radiotherapy treatment protocols. The influence of finer CT slice thickness reconstruction (STR) and resultant increased resolution DRRs on physician setup accuracy was prospectively evaluated.
  
  
  METHODS
  Four head and neck patient CT-simulation images were acquired and used to create DRR cohorts by varying STRs at 0.5, 1, 2, 2.5, and 3 mm. DRRs were displaced relative to a fixed isocenter using 0-5 mm random shifts in the three cardinal axes. Physician observers reviewed DRRs of varying STRs and displacements and then aligned reference and test DRRs replicating daily KV imaging workflow. A total of 1,064 images were reviewed by four blinded physicians. Observer errors were analyzed using nonparametric statistics (Friedman's test) to determine whether STR cohorts had detectably different displacement profiles. Post hoc bootstrap resampling was applied to evaluate potential generalizability.
  
  
  RESULTS
  The observer-based trial revealed a statistically significant difference between cohort means for observer displacement vector error ([Formula: see text]) and for [Formula: see text]-axis [Formula: see text]. Bootstrap analysis suggests a 15% gain in isocenter translational setup error with reduction of STR from 3 mm to [Formula: see text]2 mm, though interobserver variance was a larger feature than STR-associated measurement variance.
  
  
  CONCLUSIONS
  Higher resolution DRRs generated using finer CT scan STR resulted in improved observer performance at shift detection and could decrease operator-dependent geometric error. Ideally, CT STRs [Formula: see text]2 mm should be utilized for DRR generation in the head and neck.
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.|Department of Radiation Oncology, The University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Jared D
authors.initials: JD
authors.lastname: Sturgeon
authors.affiliation: Department of Radiation Oncology, The University of Texas Medical Branch, Galveston, TX, USA.|Department of Radiation Oncology, Indiana University School of Medicine, Indianapolis, IN, USA.
authors.forename: John A
authors.initials: JA
authors.lastname: Cox
authors.affiliation: Department of Radiation Oncology, The University of Texas Medical Branch, Galveston, TX, USA.
authors.forename: Lauren L
authors.initials: LL
authors.lastname: Mayo
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.
authors.forename: G Brandon
authors.initials: GB
authors.lastname: Gunn
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.
authors.forename: Lifei
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.|The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA.
authors.forename: Peter A
authors.initials: PA
authors.lastname: Balter
authors.affiliation: Scripps Proton Therapy Center, San Diego, CA, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.
authors.forename: Musaddiq
authors.initials: M
authors.lastname: Awan
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.|Department of Radiation Oncology, Şişli Etfal Teaching and Research Hospital, Istanbul, Turkey.
authors.forename: Esengul
authors.initials: E
authors.lastname: Kocak-Uzel
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.|Department of Clinical Oncology and Nuclear Medicine, Faculty of Medicine, Alexandria University, Alexandria, Egypt.
authors.forename: Abdallah Sherif Radwan
authors.initials: AS
authors.lastname: Mohamed
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA.
authors.forename: David I
authors.initials: DI
authors.lastname: Rosenthal
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd., Unit 97, Houston, TX, 77030, USA. cdfuller@mdanderson.org.|The University of Texas Graduate School of Biomedical Sciences, Houston, TX, USA. cdfuller@mdanderson.org.
authors.forename: Clifton David
authors.initials: CD
authors.lastname: Fuller
mesh_terms: D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D006801:Humans; D011857:Radiographic Image Interpretation, Computer-Assisted; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed
keywords: IGRT; Image informatics; Image-guided radiotherapy; Quality assurance; Setup error