title: Quantifying interfraction and intrafraction tumor motion in lung stereotactic body radiotherapy using respiration-correlated cone beam computed tomography.
abstract: OBJECTIVE
  Stereotactic body radiation therapy (SBRT) is an effective treatment for medically inoperable Stage I non-small-cell lung cancer. However, changes in the patient's breathing patterns during the course of SBRT may result in a geographic miss or an overexposure of healthy tissues to radiation. However, the precise extent of these changes in breathing pattern is not well known. We evaluated the inter- and intrafractional changes in tumor motion amplitude (DeltaM) over an SBRT course.
  
  
  METHODS
  Eighteen patients received image-guided SBRT delivered in three fractions; this therapy was done with abdominal compression in four patients. For each fraction, cone beam computed tomography (CBCT) was performed for tumor localization (+/- 3-mm tolerance) and then repeated to confirm geometric accuracy. Additional CBCT images were acquired at the midpoint and end of each SBRT fraction. Respiration-correlated CBCT (rcCBCT) reconstructions allowed retrospective assessment of inter- and intrafractional DeltaM by a comparison of tumor displacements in all four-dimensional CT and rcCBCT scans. The DeltaM was measured in mediolateral, superior-inferior, and anterior-posterior directions.
  
  
  RESULTS
  A total of 201 rcCBCT images were analyzed. The mean time from localization of the tumor to the end-fraction CBCT was 35 +/- 7 min. Compared with the motion recorded on four-dimensional CT, the mean DeltaM was 0.4, 1.0, and 0.4 mm, respectively, in the mediolateral, superior-inferior, and anterior-posterior directions. On treatment, the observed DeltaM was, on average, <1 mm; no DeltaM was statistically different with respect to the initial rcCBCT. However, patients in whom abdominal compression was used showed a statistically significant difference (p < 0.05) in the variance of DeltaM with respect to the initial rcCBCT in the superior-inferior direction.
  
  
  CONCLUSIONS
  The inter- and intrafractional DeltaM that occur during a course of lung SBRT are small. However, abdominal compression causes larger variations in the time spent on the treatment couch and in the inter- and intrafractional DeltaM values.
authors.affiliation: Radiation Medicine Program, Princess Margaret Hospital, University Health Network, Toronto, Ontario, Canada. jean-pierre.bissonnette@rmp.uhn.on.ca
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Bissonnette
authors.forename: Kevin N
authors.initials: KN
authors.lastname: Franks
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Purdie
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Moseley
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
authors.forename: David A
authors.initials: DA
authors.lastname: Jaffray
authors.forename: Laura A
authors.initials: LA
authors.lastname: Dawson
authors.forename: Andrea
authors.initials: A
authors.lastname: Bezjak
mesh_terms: D000005:Abdomen; D000465:Algorithms; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003250:Constriction; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000601:surgery; D009068:Movement; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D013997:Time Factors; D047368:Tumor Burden