title: Penile bulb imaging.
abstract: OBJECTIVE
  Because of the apparent relationship between potency loss and radiation doses to the erectile bodies, there is increasing rationale for incorporating penile bulb dosimetry into treatment planning and posttreatment evaluation. Because the location and shape of the penile bulb have not been described in detail on various imaging modalities, we herein describe the anatomic boundaries of the penile bulb on computed tomography (CT), magnetic resonance imaging (MR), and transrectal ultrasound (TRUS), before and after brachytherapy.
  
  
  METHODS
  Nonenhanced axial CT images were taken on a CTi CT Scanner (General Electric Medical Systems, Milwaukee, WI) with the patient in the supine position. Settings were at 300 ma, 140 kvp, 4-s scan time per slice, and collimation of 3 mm with data obtained at 3-mm intervals. Nonenhanced MR images were obtained with a 1.5 Tesla Signa Horizon LX Scanner using fast spin-echo T1-weighted (TR/TE, 466/20) and T2-weighted (TR/TE, 8000/90) images, with a slice thickness of 2 mm and an interslice gap of 0.5 mm. TRUS images were obtained with a Siemens SONOLINE Prima ultrasound machine at 6.0 MHz and a Winston-Barzell stepper unit.
  
  
  RESULTS
  The penile bulb is best visualized on T2-weighted MR images in the axial, sagittal, and coronal planes, appearing as an oval-shaped, hyperintense midline structure. On axial CT imaging, the bulb of the penis is typically readily identifiable, bounded by the paired crura laterally, the corpora spongiosum anteriorly, and the levator ani posteriorly. The penile bulb is typically well visualized on transverse TRUS, but usually only faintly seen on sagittal TRUS. The bulb is partially obscured on postimplant CT and MR images, presumably because of implant-related edema. Bulb volumes vary markedly from patient to patient, ranging from 5.6 to 12.4 cc (median: 8.1 cc).
  
  
  CONCLUSIONS
  Closer attention to penile erectile tissue doses should lead to improved external beam radiation and brachytherapy delivery. It will benefit the radiation oncology community to become familiar with these imaging findings, so that penile bulb dosimetry can be incorporated into our daily practice.
authors.affiliation: Department of Radiation Oncology, Department of Veterans Affairs, Puget Sound Health Care System, Seattle, WA 98108-1597, USA.
authors.forename: Kent E
authors.initials: KE
authors.lastname: Wallner
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Merrick
authors.forename: Mark L
authors.initials: ML
authors.lastname: Benson
authors.forename: Wayne M
authors.initials: WM
authors.lastname: Butler
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Maki
authors.forename: Bryan G
authors.initials: BG
authors.lastname: Tollenaar
mesh_terms: D006801:Humans; D008297:Male; D008953:Models, Anatomic; D010410:Penile Erection; D010413:Penis / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000528:radiation effects; D011467:Prostate / Q000528:radiation effects; D011880:Radiotherapy Planning, Computer-Assisted; D014057:Tomography, X-Ray Computed