title: Using CT imaging to delineate the prostatic apex for radiation treatment planning.
abstract: OBJECTIVE
  In computed tomography (CT)-based radiotherapy planning for prostate cancer, it is difficult to precisely delineate the prostatic apex because of its relationship with the urogenital diaphragm and bulbospongiosus musculature. In this retrospective study, we analyzed the magnetic resonance imaging (MRI) and CT scans of the patients with prostate cancer to investigate the relationship between the prostatic apex and the anatomic structure visible on CT, and to provide evidence for localizing the prostatic apex in radiotherapy planning.
  
  
  METHODS
  MRI and CT scans of 108 patients with prostate cancer were analyzed to measure the distances between the prostatic apex and the bottom of ischial tuberosities, the bottom of obturator foramen, the bottom of pubic symphysis, and the bulb of the penis. The volume of the prostate was measured to analyze its relationship with the localization of the prostatic apex.
  
  
  RESULTS
  The prostatic apex was located (13.1±3.3) mm above the bulb of the penis, (11.0±5.4) mm above the bottom of the obturator foramen, (31.3±5.5) mm above the ischial tuberosities, and (7.1±4.7) mm above the bottom of the symphysis pubis. There was no correlation between the size of the prostate and the localization of the prostatic apex.
  
  
  CONCLUSIONS
  The variance of the distance between the prostatic apex and the bulb of the penis is smaller than that of the distance between the apex and bony anatomy. Delineating the target to 6 mm above the bulb of the penis can cover the prostatic apex in 95% of the patients with prostate cancer, delineating to the bottom of obturator foramen can cover the prostatic apex in 100% of the patients.
authors.affiliation: Department of Radiation Oncology, Peking University First Hospital, Beijing 100034, PR China.
authors.forename: Xiao-Mei
authors.initials: XM
authors.lastname: Li
authors.forename: Xian-Shu
authors.initials: XS
authors.lastname: Gao
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Guo
authors.forename: Ya-Gang
authors.initials: YG
authors.lastname: Li
authors.forename: Xiao-Ying
authors.initials: XY
authors.lastname: Wang
mesh_terms: D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D010413:Penis / Q000000981:diagnostic imaging / Q000473:pathology; D011467:Prostate / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D011630:Pubic Bone / Q000000981:diagnostic imaging / Q000473:pathology; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed / Q000379:methods*