title: Assessment of gross tumor volume regression and motion changes during radiotherapy for non-small-cell lung cancer as measured by four-dimensional computed tomography.
abstract: OBJECTIVE
  To investigate the magnitudes of the changes in mobility and volume of locally advanced non-small-cell lung cancer (NSCLC) tumors during radiotherapy, using four-dimensional computed tomography (4DCT).
  
  
  METHODS
  Five to ten 4DCT data sets were acquired weekly for each of 8 patients throughout treatment. Gross tumor volumes (GTVs) were outlined on each data set. Volumes and coordinates of the GTV centroids were calculated at the 0 (end-inspiration) and 50% (end-expiration) respiration phases. Trends in magnitudes of intrafraction and interfraction positional variations were assessed for the GTV and internal target volume (ITV) during treatment.
  
  
  RESULTS
  Tumor volume reduction ranged from 20% to 71% (end-inspiration) and from 15% to 70% (end-expiration). Increased tumor mobility was observed in the superior-inferior and anterior-posterior directions. However, no trends in tumor motion were observed. Motion along the superior-inferior direction was significantly greater (p < 0.001), with mean +/- SD values of 0.86 +/- 0.19 cm, as compared with 0.39 +/- 0.08 cm and 0.19 +/- 0.05 cm in the anterior-posterior and right-left directions, respectively. A marginally significant (p = 0.049) increase in total GTV positional variation was observed with increasing treatment weeks, and similar results were seen for the interfractional ITV mobility.
  
  
  CONCLUSIONS
  Because of changes in tumor size and mobility, an explicit initial determination of the ITV may not be sufficient, especially where small setup margins are used. Repeat 4DCT scans might be warranted for highly mobile tumors to reduce the potential for missing the tumor.
authors: Division of Radiation Oncology, Department of Radiation Physics, University of Texas M.D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX 77030, USA. kbritton@mdanderson.org
authors: Keith R
authors: KR
authors: Britton
authors: George
authors: G
authors: Starkschall
authors: Susan L
authors: SL
authors: Tucker
authors: Tinsu
authors: T
authors: Pan
authors: Christopher
authors: C
authors: Nelson
authors: Joe Y
authors: JY
authors: Chang
authors: James D
authors: JD
authors: Cox
authors: Radhe
authors: R
authors: Mohan
authors: Ritsuko
authors: R
authors: Komaki
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D009068:Movement; D011446:Prospective Studies; D020266:Radiotherapy, Conformal; D014057:Tomography, X-Ray Computed / Q000379:methods*