title: Gross tumour volume variations in primary non-small-cell lung cancer during the course of treatment with stereotactic body radiation therapy.
abstract: BACKGROUND
  We aim to quantify the variations in the gross tumour volume (GTV) during a course of stereotactic body radiotherapy (SBRT) and determine its impact on dosimetric coverage of the GTV.
  
  
  METHODS
  The GTVs and dose coverage for 14 patients with 16 primary non-small-cell lung tumours treated with SBRT were investigated. Initial GTVs were calculated from treatment planning CT scans. The prescribed doses ranged from 48 to 60 Gy in three to five fractions. Before each treatment, patients underwent a CBCT scan. For each CBCT scan, the GTV and the dose received by the GTV were determined and followed during the course of therapy.
  
  
  RESULTS
  There was considerable variation in the measured GTVs during the course of therapy. Increases of up to 63.3% of volume measured by initial CBCT were detected during the first few fractions, after which GTV tended to decrease. Dose coverage (V95) for any given fraction deviated no more than 5% from optimised coverage obtained in the initial treatment plan. In the long term, all patients with follow-up scans demonstrated tumour shrinkage with no radiographic evidence of tumour recurrence.
  
  
  CONCLUSIONS
  GTV, as evaluated in this study, demonstrates an initial increase in volume followed by a subsequent decrease. This volume change needs to be considered in the design of treatment plans and assignment of treatment margins.
authors.affiliation: Department of Radiation Oncology, Stephenson Cancer Center, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma, USA.
authors.forename: T
authors.initials: T
authors.lastname: Gunter
authors.forename: I
authors.initials: I
authors.lastname: Ali
authors.forename: C
authors.initials: C
authors.lastname: Matthiesen
authors.forename: M
authors.initials: M
authors.lastname: Machiorlatti
authors.forename: D
authors.initials: D
authors.lastname: Thompson
authors.forename: O
authors.initials: O
authors.lastname: Algan
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D016634:Radiosurgery / Q000379:methods*; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome; D047368:Tumor Burden / Q000528:radiation effects*
keywords: interfractional tumour volume variation; non-small-cell lung cancer; stereotactic body radiation therapy