title: Definition of the CTV prostate in CT and MRI by using CT-MRI image fusion in IMRT planning for prostate cancer.
abstract: OBJECTIVE
  To determine the prostate volumes defined by using MRI and CT scans, as well as the difference between prostate delineation in MRI and CT in three dimensions (3D). A further goal was to use MRI to identify subgroups of patients in whom seminal vesicle irradiation can be avoided.
  
  
  METHODS
  A total of 294 patients with biopsy-proven prostate cancer (MRI stages: T(1), 16 [5%]; T(2), 84 [29%]; T(3), 191 [65%]; T(4), 3 [1%]) underwent pelvic CT and MRI scans before intensity-modulated radiation therapy (IMRT) planning. 3D images were used to compare the prostate volumes defined by superimposed MR and CT images. Prostate volumes were calculated in cm(3).
  
  
  RESULTS
  The mean prostate volume defined by MRI (44.3 cm(3) [range, 8.8-182.8 cm(3)]) was 35% smaller than that defined by CT (68.5 cm(3) [range, 15.2-241.3 cm(3)]). The areas of nonagreement were observed predominantly in the most superior and inferior portions of the prostate. The incidence of seminal vesicle invasion (SVI) identified by MRI was 63% (n = 182 of 290). The median length of SVI was 2.6 cm (range, 1.1-4.7 cm; 62% of the median SV length). The low-risk patients (59%, n = 171 of 290) calculated by applying the Roach and Diaz formula had a SVI rate of 57% (n = 97 of 171), the high-risk patients (41%, n = 119 of 290) of 71% (n = 85 of 119).
  
  
  CONCLUSIONS
  Compared with MRI, CT scans overestimate prostate volume by 35%. CT-MRI image fusion-based treatment planning allows more accurate prediction of the correct staging and more precise target volume identification in prostate cancer patients.
authors.affiliation: Department of Radiation Oncology and Radiotherapy, Südharz-Krankenhaus, Nordhausen, Germany. bettina.hentschel@shk-ndh.de
authors.forename: Bettina
authors.initials: B
authors.lastname: Hentschel
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Oehler
authors.forename: Dirk
authors.initials: D
authors.lastname: Strauss
authors.forename: Andreas
authors.initials: A
authors.lastname: Ulrich
authors.forename: Ansgar
authors.initials: A
authors.lastname: Malich
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008207:Lymphatic Metastasis / Q000473:pathology / Q000532:radiotherapy; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D009929:Organ Size; D011467:Prostate / Q000528:radiation effects; D011471:Prostatic Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012669:Seminal Vesicles / Q000528:radiation effects; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden