title: Daily cone-beam computed tomography used to determine tumour shrinkage and localisation in lung cancer patients.
abstract: OBJECTIVE
  Daily Cone-beam computed tomography (CBCT) in room imaging is used to determine tumour shrinkage during a full radiotherapy (RT) course. In addition, relative interfractional tumour and lymph node motion is determined for each RT fraction.
  
  
  METHODS
  From November 2009 to March 2010, 20 consecutive lung cancer patients (14 NSCLC, 6 SCLC) were followed with daily CBCT during RT. The gross tumour volume for lung tumour (GTV-t) was visible in all daily CBCT scans and was delineated at the beginning, at the tenth and the 20th fraction, and at the end of treatment. Whenever visible, the gross tumour volume for lymph nodes (GTV-n) was also delineated. The GTV-t and GTV-n volumes were determined. All patients were setup according to an online bony anatomy match. Retrospectively, matching based on the internal target volume (ITV), the GTV-t or the GTV-n was performed.
  
  
  RESULTS
  In eight patients, we observed a significant GTV-t shrinkage (15-40%) from the planning CT until the last CBCT. Only five patients presented a significant shrinkage (21-37%) in the GTV-n. Using the daily CBCT imaging, it was found that the mean value of the difference between a setup using the skin tattoo and an online matching using the ITV was 7.3±2.9 mm (3D vector in the direction of ITV). The mean difference between the ITV and bony anatomy matching was 3.0±1.3 mm. Finally, the mean distance between the GTV-t and the GTV-N was 2.9±1.6 mm.
  
  
  CONCLUSIONS
  One third of all patients with lung cancer undergoing chemo-RT achieved significant tumour shrinkage from planning CT until the end of the radiotherapy. Differences in GTV-t and GTV-n motion was observed and matching using the ITV including both GTV-t and GTV-n is therefore preferable.
authors.affiliation: Aarhus University Hospital, Department of Oncology, Aarhus, Denmark. mariknap@rm.dk
authors.forename: Marianne Marquard
authors.initials: MM
authors.lastname: Knap
authors.forename: Lone
authors.initials: L
authors.lastname: Hoffmann
authors.forename: Marianne
authors.initials: M
authors.lastname: Nordsmark
authors.forename: Anne
authors.initials: A
authors.lastname: Vestergaard
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D002940:Circadian Rhythm / Q000502:physiology; D003131:Combined Modality Therapy; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D018450:Disease Progression; D019583:Dose Fractionation, Radiation; D005500:Follow-Up Studies; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy*; D009367:Neoplasm Staging; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D012189:Retrospective Studies; D055752:Small Cell Lung Carcinoma / Q000000981:diagnostic imaging / Q000188:drug therapy / Q000473:pathology / Q000532:radiotherapy; D013997:Time Factors; D047368:Tumor Burden / Q000528:radiation effects