title: Comparison of rigid and adaptive methods of propagating gross tumor volume through respiratory phases of four-dimensional computed tomography image data set.
abstract: OBJECTIVE
  To compare three different methods of propagating the gross tumor volume (GTV) through the respiratory phases that constitute a four-dimensional computed tomography image data set.
  
  
  METHODS
  Four-dimensional computed tomography data sets of 20 patients who had undergone definitive hypofractionated radiotherapy to the lung were acquired. The GTV regions of interest (ROIs) were manually delineated on each phase of the four-dimensional computed tomography data set. The ROI from the end-expiration phase was propagated to the remaining nine phases of respiration using the following three techniques: (1) rigid-image registration using in-house software, (2) rigid image registration using research software from a commercial radiotherapy planning system vendor, and (3) rigid-image registration followed by deformable adaptation originally intended for organ-at-risk delineation using the same software. The internal GTVs generated from the various propagation methods were compared with the manual internal GTV using the normalized Dice similarity coefficient (DSC) index.
  
  
  RESULTS
  The normalized DSC index of 1.01 +/- 0.06 (SD) for rigid propagation using the in-house software program was identical to the normalized DSC index of 1.01 +/- 0.06 for rigid propagation achieved with the vendor's research software. Adaptive propagation yielded poorer results, with a normalized DSC index of 0.89 +/- 0.10 (paired t test, p <0.001).
  
  
  CONCLUSIONS
  Propagation of the GTV ROIs through the respiratory phases using rigid- body registration is an acceptable method within a 1-mm margin of uncertainty. The adaptive organ-at-risk propagation method was not applicable to propagating GTV ROIs, resulting in an unacceptable reduction of the volume and distortion of the ROIs.
authors.affiliation: Division of Radiation Oncology, Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. veniezhil@hotmail.com
authors.forename: Muthuveni
authors.initials: M
authors.lastname: Ezhil
authors.forename: Bum
authors.initials: B
authors.lastname: Choi
authors.forename: George
authors.initials: G
authors.lastname: Starkschall
authors.forename: M Kara
authors.initials: MK
authors.lastname: Bucci
authors.forename: Sastry
authors.initials: S
authors.lastname: Vedam
authors.forename: Peter
authors.initials: P
authors.lastname: Balter
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D045853:Exhalation; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden