title: Four-dimensional multislice computed tomography for determination of respiratory lung tumor motion in conformal radiotherapy.
abstract: OBJECTIVE
  We used four-dimensional multislice spiral computed tomography (MSCT) to determine respiratory lung-tumor motion and compared this strategy to common clinical practice in conformal radiotherapy treatment-planning imaging.
  
  
  METHODS
  The entire lung volume of 10 consecutive patients with 14 lung metastases were scanned by a 16-slice MSCT. During the scans, patients were instructed to breathe through a spirometer that was connected to a laptop computer. For each patient, 10 stacks of 1.5-mm slices, equally distributed throughout the respiratory cycle, were reconstructed from the acquired MSCT data. The lung tumors were manually contoured in each data set. For each patient, the tumor-volume contours of all data sets were copied to 1 data set, which allowed determination of the volume that encompassed all 10 lung-tumor positions (i.e., the tumor-traversed volume [TTV]) during the respiratory cycle. The TTV was compared with the 10 tumor volumes contoured for each patient, to which an empiric respiratory-motion margin was added. The latter target volumes were designated internal-motion included tumor volume (IMITV).
  
  
  RESULTS
  The TTV measurements were significantly smaller than the reference IMITV measurements (5.2 +/- 10.2 cm(3) and 10.1 +/- 13.7 cm(3), respectively). All 10 IMITVs for 2 of the 4 tumors in 1 subject completely encompassed the TTV. All 10 IMITVs for 3 tumors in 2 patients did not show overlap with up to 35% of the corresponding TTV. The 10 IMITVs for the remaining tumors either completely encompassed the corresponding TTV or did not show overlap with up to 26% of the corresponding TTV.
  
  
  CONCLUSIONS
  We found that individualized determination of respiratory lung-tumor motion by four-dimensional respiratory-gated MSCT represents a better and simple strategy to incorporate periodic physiologic motion compared with a generalized approach. The former strategy can, therefore, improve common and state-of-the-art clinical practice in conformal radiotherapy.
authors.affiliation: Department of Radiotherapy, Erasmus Medical Center, Rotterdam, The Netherlands. emleter@hotmail.com
authors.forename: Edward M
authors.initials: EM
authors.lastname: Leter
authors.forename: Filippo
authors.initials: F
authors.lastname: Cademartiri
authors.forename: Peter C
authors.initials: PC
authors.lastname: Levendag
authors.forename: Thomas
authors.initials: T
authors.lastname: Flohr
authors.forename: Henk
authors.initials: H
authors.lastname: Stam
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Nowak
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000556:secondary; D008297:Male; D008875:Middle Aged; D009068:Movement; D020266:Radiotherapy, Conformal; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods*