title: Comparison of 2 transabdominal ultrasound image guidance techniques for prostate and prostatic fossa radiation therapy.
abstract: OBJECTIVE
  Our clinic is a long-term user of a first-generation transabdominal (TA) biplanar (2.5-dimensional [2.5D]) ultrasound image guidance (USIG) system for prostate cancer treatments. We are also an early adopter and development partner for a new, second-generation, fully 3D USIG system that allows for volumetric TA localization of the prostate. This new system has been evaluated at our institution by direct comparison with the previously established first-generation TA method for prostate alignment.
  
  
  METHODS
  We compared the 2 TA-USIG methods on the same subjects and same treatment sessions. A total of 1428 fractions delivered to 41 treated patients (16 intact prostate, 25 fossa) were analyzed regarding the agreement of alignments between the 2 US positioning systems. Patients were first aligned to tattoos using treatment room lasers. TA-USIG using the 3D system was then performed to align contours derived during the computed tomography simulation process to their corresponding daily US-visualized structures. The US-3D system image guidance shifts were performed and recorded as the "initial" shifts. A 2.5D system alignment was then immediately performed using the same computed tomography derived reference contours and the indicated shifts, relative to the 3D system, were recorded as the difference between the 2 alignment methods.
  
  
  RESULTS
  The average difference between the 2 TA-USIG alignments for all patients was 0.4 ± 0.7 mm, 0.7 ± 0.9 mm, and 0.5 ± 0.9 mm in the left-right, anteroposterior, and superoinferior directions, respectively. No significant difference in system agreement between intact prostate versus fossa patients was observed.
  
  
  CONCLUSIONS
  Our comparison of an established 2.5D USIG method with a newer, fully 3D approach for prostate alignment of 41 different patients (1428 fractions) shows excellent agreement with each other, despite the nontrivial difference in imaging approaches. This shows that the 2 specific USIG approaches yield results that are consistent with each other, and that the USIG modality yields consistent results within the modality.
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah. Electronic address: bill.salter@hci.utah.edu.
authors.forename: Bill J
authors.initials: BJ
authors.lastname: Salter
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Martin
authors.initials: M
authors.lastname: Szegedi
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Christine
authors.initials: C
authors.lastname: Boehm
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Vikren
authors.initials: V
authors.lastname: Sarkar
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Prema
authors.initials: P
authors.lastname: Rassiah-Szegedi
authors.affiliation: Department of Radiation Oncology, University of Louisville, Louisville, Kentucky.
authors.forename: Brian
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Hui
authors.initials: H
authors.lastname: Zhao
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Jessica
authors.initials: J
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Long
authors.initials: L
authors.lastname: Huang
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Kris
authors.initials: K
authors.lastname: Kokeny
authors.affiliation: Department of Radiation Oncology, University of Utah, Salt Lake City, Utah.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Tward
mesh_terms: D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D056888:Patient Positioning / Q000379:methods*; D011467:Prostate / Q000000981:diagnostic imaging*; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided / Q000379:methods*; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography