title: Development of 3-dimensional transperineal ultrasound for image guided radiation therapy of the prostate: Early evaluations of feasibility and use for inter- and intrafractional prostate localization.
abstract: OBJECTIVE
  Transperineal ultrasound (TPUS) allows for continuous imaging of the prostate gland, but the accuracy of TPUS has not been rigorously studied. We determined the feasibility of prostate imaging with TPUS and subsequently compared prostate localization with TPUS and computed tomography (CT).
  
  
  METHODS
  We completed 2 sequential evaluations of TPUS. The feasibility study included 15 men with localized prostate cancer and tested if TPUS adequately imaged the prostate. Image qualities of the prostate and adjacent normal structures were measured. The subsequent study included 17 men who at the time of initial radiation treatment planning and in 3 subsequent sessions had CT and TPUS imaging performed and compared.
  
  
  RESULTS
  Feasibility of TPUS was confirmed in the first trial. After expected hardware and software modifications were completed, TPUS provided near complete edge definition of the prostate in the final 5 patients in the feasibility trial. The second study allowed for the comparison of 30 image sets. The differences between TPUS and CT in each direction (mean + standard deviation) were found to be 0.06 ± 2.86 mm (anteroposterior), 0.49 ± 3.49 mm (superoinferior), and 0.63 ± 3.27 mm (left-right), with no significant difference between the 2 modalities (all P > .32). The Euclidean distance variance using the 2 techniques was 5.25 ± 1.79 mm, which was significantly different.
  
  
  CONCLUSIONS
  TPUS provides good imaging of the prostate gland. We noted excellent correlation in gland localization when TPUS is compared with CT scans when comparing routine 3-dimensional positional data. Euclidean distance variation suggests the potential that summation of small errors may in fact lead to significant differences in actual gland positional certainty. The reported difference is within the range of standard planning target volume expansion however requires additional evaluation.
authors.affiliation: Medical student, University of Vermont College of Medicine, Burlington, Vermont.
authors.forename: Apoorva
authors.initials: A
authors.lastname: Trivedi
authors.affiliation: Medical Biostatistics, University of Vermont College of Medicine, Burlington, Vermont.
authors.forename: Takamura
authors.initials: T
authors.lastname: Ashikaga
authors.affiliation: Radiation Oncology, University of Vermont Medical Center, Burlington, Vermont.
authors.forename: Daphne
authors.initials: D
authors.lastname: Hard
authors.affiliation: Radiation Oncology, University of Vermont Medical Center, Burlington, Vermont.
authors.forename: Jessica
authors.initials: J
authors.lastname: Archambault
authors.affiliation: Elekta, Montreal, Quebec, Canada.
authors.forename: Martin
authors.initials: M
authors.lastname: Lachaine
authors.affiliation: Elekta, Montreal, Quebec, Canada.
authors.forename: David T
authors.initials: DT
authors.lastname: Cooper
authors.affiliation: Medical Biostatistics, University of Vermont College of Medicine, Burlington, Vermont; University of Vermont Cancer Center, Burlington, Vermont. Electronic address: James.Wallace@uvmhealth.org.
authors.forename: Harold James
authors.initials: HJ
authors.lastname: Wallace
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D010502:Perineum / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D061089:Radiotherapy, Image-Guided; D014057:Tomography, X-Ray Computed; D014463:Ultrasonography