title: Changes in penile bulb dose when using the Clarity transperineal ultrasound probe: A planning study.
abstract: OBJECTIVE
  The Clarity system allows monitoring of intrafraction target organ movements in external beam radiation therapy of prostate cancer by using transperineal ultrasound. The probe positioning at the perineum could lead to a compression and shift of the penile bulb (PB) toward the high-dose region. Dose to the PB has been reported to be associated with the risk of posttreatment erectile dysfunction. This planning study reports on PB translations and changes in volume and dose when applying the transperineal ultrasound probe.
  
  
  METHODS
  For 10 patients treated with external beam radiation therapy for prostate cancer between 2013 and 2014, a planning computed tomography scan with and without the ultrasound probe in place was acquired. The planning target volume and organs at risk including the PB were contoured in the computed tomography scan with and without the probe. Radiation therapy plans for both scenarios were calculated. In a second step, for planning with the probe in position, an additional objective for improved sparing of the PB was introduced.
  
  
  RESULTS
  The median PB volume was 5.5 mL (range, 3.8-7.1 mL) without the probe and 3.5 mL (range, 2.0-5.8 mL) with the probe. The median shift of the PB was 1 mm in the posterior (range, 3 mm posterior-2 mm anterior) and 6 mm in the superior direction (range, 0-14 mm superior), with no relevant shift of the prostate. The median mean dose in 95% of the PB was 34.1 Gy (range, 6.0-50.4 Gy), 48.3 Gy (range, 7.2-56.8 Gy), and 39.4 Gy (range, 5.6-51.3 Gy) for plans without probe, with probe, and with probe and additional planning objective, respectively.
  
  
  CONCLUSIONS
  Dose to the PB increased when using the transperineal probe. After introducing an additional plan-optimization objective for PB sparing, dose-volume parameters were below Quantitative Analyses of Normal Tissue Effects in the Clinic thresholds for all but one patient.
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany. Electronic address: mantel_f@ukw.de.
authors.forename: Frederick
authors.initials: F
authors.lastname: Mantel
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Richter
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Groh
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Ingulf
authors.initials: I
authors.lastname: Lawrenz
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weick
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Bülent
authors.initials: B
authors.lastname: Polat
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany; Department of Radiation Oncology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Guckenberger
authors.affiliation: Department of Radiation Oncology, University Hospital Wuerzburg, Wuerzburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Flentje
mesh_terms: D006801:Humans; D008297:Male; D058958:Organs at Risk; D010413:Penis / Q000000981:diagnostic imaging*; D010502:Perineum; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D014463:Ultrasonography