title: Variation in Lung Tumour Breathing Motion between Planning Four-dimensional Computed Tomography and Stereotactic Ablative Radiotherapy Delivery and its Dosimetric Implications: Any Role for Four-dimensional Set-up Verification?
abstract: OBJECTIVE
  To investigate variation in tumour breathing motion (TBM) between the planning four-dimensional computed tomograph (4DCT) and treatment itself for primary or secondary lung tumours undergoing stereotactic ablative radiotherapy (SABR).
  
  
  METHODS
  Sixteen consecutive patients underwent planning 4DCT at least 1 week after implantation of a fiducial marker. The maximal extent of breathing motion of the intra-tumoural fiducial was measured at 4DCT and again at delivery of each SABR fraction on the linac using stereoscopic kilovoltage imaging. Displacements of the fiducial beyond planned limits were measured in three dimensions and represented as vectors. Variation in breathing motion between the planning 4DCT and treatment, and between individual SABR fractions was analysed.
  
  
  RESULTS
  Although TBM at treatment exceeded planned tumour motion limits for at least part of the course for all patients, 31% of patients remained consistently within 1 mm, 50% within 2 mm and 69% consistently within 3 mm of planned parameters. However, 19% of patients experienced TBM variation 5 mm or more beyond planned limits for at least one fraction. For all patients, the median displacement vector at treatment beyond the planned motion envelope was 1.0 mm (mean 2.0 mm, range 0-12.7 mm). Variation in TBM at treatment from 4DCT correlated neither with the magnitude of TBM at 4DCT nor with planning target volume size (rs = 0.13, P = 0.62; rs = 0.02, P = 0.94, respectively). Nor was TBM variation related to tumour type or lobar position (P = 0.35, P = 0.06, respectively). Inter-fraction TBM variation was modest, with an average standard deviation of 1.7 mm (0.3-8.7 mm).
  
  
  CONCLUSIONS
  TBM variation between 4DCT and treatment and between SABR fractions was modest for most patients. However, 19% of patients experienced significant TBM variation that could be clinically relevant for those most severely affected. It seems prudent to carry out on-couch assessment of TBM at each SABR fraction to identify such patients who might benefit from respiratory gating or adaptive radiotherapy to maintain tumour motion within the planned limits.
authors.affiliation: Department of Surgery, Monash University, Melbourne, Australia; William Buckland Radiotherapy Centre, The Alfred Hospital, Prahran, Australia. Electronic address: Jeremy.ruben@wbrc.org.au.
authors.forename: J D
authors.initials: JD
authors.lastname: Ruben
authors.affiliation: William Buckland Radiotherapy Centre, The Alfred Hospital, Prahran, Australia.
authors.forename: A
authors.initials: A
authors.lastname: Seeley
authors.affiliation: William Buckland Radiotherapy Centre, The Alfred Hospital, Prahran, Australia.
authors.forename: V
authors.initials: V
authors.lastname: Panettieri
authors.affiliation: William Buckland Radiotherapy Centre, The Alfred Hospital, Prahran, Australia; Department of Physics, Royal Melbourne Institute of Technology, Melbourne, Australia.
authors.forename: T
authors.initials: T
authors.lastname: Ackerly
mesh_terms: D000328:Adult; D000368:Aged; D016477:Artifacts; D005260:Female; D057918:Fiducial Markers; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009038:Motion; D011874:Radiometry / Q000379:methods; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration
keywords: Breathing motion; SABR; breathing movement; respiratory motion; stereotactic ablative radiotherapy