title: An assessment of cone beam CT in the adaptive radiotherapy planning process for non-small-cell lung cancer patients.
abstract: OBJECTIVE
  To investigate the potential use of cone beam CT (CBCT) in adaptive radiotherapy (ART) planning process for non-small-cell lung cancer (NSCLC).
  
  
  METHODS
  17 retrospective patients with NSCLC Stage T1-T4, who had completed a course of radiotherapy with weekly CBCT imaging were selected for the study. The patients had been delineated and planned for three-dimensional (3D) conformal treatment (prescription: 55 Gy in 20 fractions) based on free-breathing four-dimensional CT data. Of these initial 17 patients, 12 had full quantitative data on gross tumour volume (GTV) position and volume throughout treatment. GTV delineation was carried out on weekly CBCT by a clinical oncologist. For each patient, mean percentage change in GTV and centre of mass (COM) displacement (based on 3D vectors) were calculated throughout treatment. Volume overlap between GTVs was calculated. Correlation of the COM displacement and planning GTV (pGTV) was assessed. A linear mixed model with patients as random effects was fitted to the data to assess potential benefit from using ART for these patients.
  
  
  RESULTS
  Comparison of CBCT-based GTV acquired prior to Fraction 1 (cbctGTV1) to pGTV showed mean 20 ± 19% volume increase using a related sample Wilcoxon signed rank test p = 0.04. Correlation was identified between volume reductions and dose delivered (beta = -0.003, p < 0.001)-a highly statistically significant association. Compared with cbctGTV1, the mean ratios ± standard deviation were cbctGTV2, 0.93 ± 0.08; cbctGTV3, 0.84 ± 0.12; and cbctGTV4, 0.75 ± 0.14. The dice similarity coefficient was 0.81 ± 0.14, 0.78 ± 0.17, 0.73 ± 0.19, respectively. The COM was consistent throughout treatment (mean 0.35 ± 0.24 cm). A fitted model predicts that a mean change of 30% volume relative to cbctGTV1 occurs at a dose of approximately 50 Gy.
  
  
  CONCLUSIONS
  Using a 30% reduction in volume, ART would not be of benefit for all radiotherapy-alone-treated patients with NSCLC assessed in this study. For individual patients and patients with atelectasis, CBCT imaging was able to identify volume change.
  
  
  CONCLUSIONS
  For patients treated with 55 Gy in 20 fractions, target volume changes throughout treatment have been demonstrated using CBCT and can be used to highlight patients who may benefit from ART.
authors.affiliation: 1 Department of Radiotherapy, Beatson West of Scotland Cancer Centre, Glasgow, UK.
authors.forename: Aileen
authors.identifier: http://orcid.org/0000-0003-2413-2561
authors.initials: A
authors.lastname: Duffton
authors.affiliation: 1 Department of Radiotherapy, Beatson West of Scotland Cancer Centre, Glasgow, UK.
authors.forename: Stephen
authors.initials: S
authors.lastname: Harrow
authors.affiliation: 1 Department of Radiotherapy, Beatson West of Scotland Cancer Centre, Glasgow, UK.
authors.forename: Carolynn
authors.initials: C
authors.lastname: Lamb
authors.affiliation: 2 Department of Clinical Physics and Bio-Engineering, Beatson West of Scotland Cancer Centre, Glasgow, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: McJury
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects