title: Radiographic and anatomic basis for prostate contouring errors and methods to improve prostate contouring accuracy.
abstract: OBJECTIVE
  Use of highly conformal radiation for prostate cancer can lead to both overtreatment of surrounding normal tissues and undertreatment of the prostate itself. In this retrospective study we analyzed the radiographic and anatomic basis of common errors in computed tomography (CT) contouring and suggest methods to correct them.
  
  
  METHODS
  Three hundred patients with prostate cancer underwent CT and magnetic resonance imaging (MRI). The prostate was delineated independently on the data sets. CT and MRI contours were compared by use of deformable registration. Errors in target delineation were analyzed and methods to avoid such errors detailed.
  
  
  RESULTS
  Contouring errors were identified at the prostatic apex, mid gland, and base on CT. At the apex, the genitourinary diaphragm, rectum, and anterior fascia contribute to overestimation. At the mid prostate, the anterior and lateral fasciae contribute to overestimation. At the base, the bladder and anterior fascia contribute to anterior overestimation. Transition zone hypertrophy and bladder neck variability contribute to errors of overestimation and underestimation at the superior base, whereas variable prostate-to-seminal vesicle relationships with prostate hypertrophy contribute to contouring errors at the posterior base.
  
  
  CONCLUSIONS
  Most CT contouring errors can be detected by (1) inspection of a lateral view of prostate contours to detect projection from the expected globular form and (2) recognition of anatomic structures (genitourinary diaphragm) on the CT scans that are clearly visible on MRI. This study shows that many CT prostate contouring errors can be improved without direct incorporation of MRI data.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, MI 48374-1236, USA. mclaughb@umich.edu
authors.forename: Patrick W
authors.initials: PW
authors.lastname: McLaughlin
authors.forename: Cheryl
authors.initials: C
authors.lastname: Evans
authors.forename: Mary
authors.initials: M
authors.lastname: Feng
authors.forename: Vrinda
authors.initials: V
authors.lastname: Narayana
mesh_terms: D003951:Diagnostic Errors / Q000517:prevention & control; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015588:Observer Variation; D010413:Penis / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011467:Prostate / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000473:pathology; D011470:Prostatic Hyperplasia / Q000000981:diagnostic imaging / Q000473:pathology; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D011631:Pubic Symphysis / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012007:Rectum / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D012669:Seminal Vesicles / Q000000981:diagnostic imaging / Q000473:pathology; D036542:Tomography, Spiral Computed / Q000379:methods*; D014521:Urethra / Q000033:anatomy & histology / Q000000981:diagnostic imaging