title: Dynamic intraoperative dosimetry for prostate brachytherapy using a nonisocentric C-arm.
abstract: OBJECTIVE
  To evaluate a prototypical system of dynamic intraoperative dosimetry for prostate brachytherapy using registered ultrasound and fluoroscopy (RUF) with a nonisocentric C-arm (GE OEC, Salt Lake City, UT) and to compare intraoperative dosimetry of RUF as well as ultrasound-based seed localization (USD) with Day 0 CT dosimetry.
  
  
  METHODS
  Seed positions were independently determined using RUF and USD. RUF uses a radio-opaque fiducial for registration to ultrasound and 3-dimensional reconstruction of seeds relative to prostate using nonisocentric C-arm fluoroscopy. Postimplant CT was performed on Day 0. Squared differences between dosimetric measures for RUF vs. CT and USD vs. CT were calculated and mean squared differences evaluated. Paired t test was used to evaluate which method was more closely aligned with CT. Accuracies of USD and RUF compared with CT were estimated using a nonparametric approach.
  
  
  RESULTS
  Six patients were treated and compared with USD. RUF identified areas of underdosage intraoperatively in all patients and median 5 additional seeds were placed. In 40 of 42 measures, RUF was equally or more closely correlated with CT than USD. USD showed statistically significant variation from CT for 6 of 7 parameters compared with 1 of 7 parameters for RUF. Mean squared differences from CT were significantly smaller for RUF in 4 of 7 parameters compared with USD.
  
  
  CONCLUSIONS
  Dynamic intraoperative dosimetry is possible with a conventional nonisocentric C-arm. Compared with an USD method, RUF-based intraoperative dosimetry was more closely aligned with immediate postimplant CT. RUF identified areas of underdosage, which were not detected using USD.
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Sciences, Johns Hopkins University, School of Medicine, Baltimore, MD 21231, USA. dsong2@jhmi.edu
authors.forename: Danny Y
authors.initials: DY
authors.lastname: Song
authors.forename: Ameet K
authors.initials: AK
authors.lastname: Jain
authors.forename: Zhe
authors.initials: Z
authors.lastname: Zhang
authors.forename: Anton
authors.initials: A
authors.lastname: Deguet
authors.forename: Yi
authors.initials: Y
authors.lastname: Le
authors.forename: Elwood
authors.initials: E
authors.lastname: Armour
authors.forename: E Clif
authors.initials: EC
authors.lastname: Burdette
authors.forename: Gabor
authors.initials: G
authors.lastname: Fichtinger
mesh_terms: D000368:Aged; D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011471:Prostatic Neoplasms / Q000175:diagnosis* / Q000532:radiotherapy*; D019919:Prosthesis Implantation / Q000379:methods*; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D025321:Surgery, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods; D016896:Treatment Outcome; D014463:Ultrasonography / Q000379:methods