title: Efficient CT simulation of the four-field technique for conformal radiotherapy of prostate carcinoma.
abstract: OBJECTIVE
  Conformal radiotherapy of prostate carcinoma relies on contouring of individual CT slices for target and normal tissue localization. This process can be very time consuming. In the present report, we describe a method to more efficiently localize pelvic anatomy directly from digital reconstructed radiographs (DRRs).
  
  
  METHODS
  Ten patients with prostate carcinoma underwent CT simulation (the spiral mode at 3 mm separation) for conformal four-field "box" radiotherapy. The bulbous urethra and bladder were opacified with iodinated contrast media. On lateral and anteroposterior DRRs, the volume of interest (VOI) was restricted to 1.0-1.5 cm tissue thickness to optimize digital radiograph reconstruction of the prostate and seminal vesicles. By removing unessential voxel elements, this method provided direct visualization of those structures. For comparison, the targets of each patient were also obtained by contouring CT axial slices.
  
  
  RESULTS
  The method was successfully performed if the target structures were readily visualized and geometrically corresponded to those generated by contouring axial images. The targets in 9 of 10 patients were reliable representations of the CT-contoured volumes. One patient had 18 mm variation due to the lack of bladder opacification. Using VOIs to generate thin tissue DRRs, the time required for target and normal tissue localization was on the average less than 5 min.
  
  
  CONCLUSIONS
  In CT simulation of the four-field irradiation technique for prostate carcinoma, thin-tissue DRRs allowed for efficient and accurate target localization without requiring individual axial image contouring. This method may facilitate positioning of the beam isocenter and provide reliable conformal radiotherapy.
authors.affiliation: Department of Radiation Oncology, Thomas Jefferson University Hospital, Bodine Center for Cancer Treatment, Philadelphia, PA 19107, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Valicenti
authors.forename: F M
authors.initials: FM
authors.lastname: Waterman
authors.forename: R J
authors.initials: RJ
authors.lastname: Croce
authors.forename: B
authors.initials: B
authors.lastname: Corn
authors.forename: N
authors.initials: N
authors.lastname: Suntharalingam
authors.forename: W J
authors.initials: WJ
authors.lastname: Curran
mesh_terms: D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012669:Seminal Vesicles / Q000000981:diagnostic imaging; D014057:Tomography, X-Ray Computed