title: Adaptive radiotherapy planning on decreasing gross tumor volumes as seen on megavoltage computed tomography images.
abstract: OBJECTIVE
  To evaluate gross tumor volume (GTV) changes for patients with non-small-cell lung cancer by using daily megavoltage (MV) computed tomography (CT) studies acquired before each treatment fraction on helical tomotherapy and to relate the potential benefit of adaptive image-guided radiotherapy to changes in GTV.
  
  
  METHODS
  Seventeen patients were prescribed 30 fractions of radiotherapy on helical tomotherapy for non-small-cell lung cancer at London Regional Cancer Program from Dec 2005 to March 2007. The GTV was contoured on the daily MVCT studies of each patient. Adapted plans were created using merged MVCT-kilovoltage CT image sets to investigate the advantages of replanning for patients with differing GTV regression characteristics.
  
  
  RESULTS
  Average GTV change observed over 30 fractions was -38%, ranging from -12 to -87%. No significant correlation was observed between GTV change and patient's physical or tumor features. Patterns of GTV changes in the 17 patients could be divided broadly into three groups with distinctive potential for benefit from adaptive planning.
  
  
  CONCLUSIONS
  Changes in GTV are difficult to predict quantitatively based on patient or tumor characteristics. If changes occur, there are points in time during the treatment course when it may be appropriate to adapt the plan to improve sparing of normal tissues. If GTV decreases by greater than 30% at any point in the first 20 fractions of treatment, adaptive planning is appropriate to further improve the therapeutic ratio.
authors.affiliation: London Regional Cancer Program, London Health Sciences Centre, London, Ontario, Canada.
authors.forename: Curtis
authors.initials: C
authors.lastname: Woodford
authors.forename: Slav
authors.initials: S
authors.lastname: Yartsev
authors.forename: A Rashid
authors.initials: AR
authors.lastname: Dar
authors.forename: Glenn
authors.initials: G
authors.lastname: Bauman
authors.forename: Jake
authors.initials: J
authors.lastname: Van Dyk
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008297:Male; D008875:Middle Aged; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D036542:Tomography, Spiral Computed; D047368:Tumor Burden