title: In vivo reproducibility of robotic probe placement for a novel ultrasound-guided radiation therapy system.
abstract: Ultrasound can provide real-time image guidance of radiation therapy, but the probe-induced tissue deformations cause local deviations from the treatment plan. If placed during treatment planning, the probe causes streak artifacts in required computed tomography (CT) images. To overcome these challenges, we propose robot-assisted placement of an ultrasound probe, followed by replacement with a geometrically identical, CT-compatible model probe. In vivo reproducibility was investigated by implanting a canine prostate, liver, and pancreas with three 2.38-mm spherical markers in each organ. The real probe was placed to visualize the markers and subsequently replaced with the model probe. Each probe was automatically removed and returned to the same position or force. Under position control, the median three-dimensional reproducibility of marker positions was 0.6 to 0.7 mm, 0.3 to 0.6 mm, and 1.1 to 1.6 mm in the prostate, liver, and pancreas, respectively. Reproducibility was worse under force control. Probe substitution errors were smallest for the prostate (0.2 to 0.6 mm) and larger for the liver and pancreas (4.1 to 6.3 mm), where force control generally produced larger errors than position control. Results indicate that position control is better than force control for this application, and the robotic approach has potential, particularly for relatively constrained organs and reproducibility errors that are smaller than established treatment margins.
authors.affiliation: Johns Hopkins University , Laboratory for Computational Sensing and Robotics, Baltimore, Maryland 21218, United States.
authors.forename: Muyinatu A
authors.initials: MA
authors.lastname: Lediju Bell
authors.affiliation: Johns Hopkins University , Laboratory for Computational Sensing and Robotics, Baltimore, Maryland 21218, United States ; Johns Hopkins University , Department of Computer Science, Baltimore, Maryland 21218, United States.
authors.forename: H Tutkun
authors.initials: HT
authors.lastname: Sen
authors.affiliation: Johns Hopkins University , Laboratory for Computational Sensing and Robotics, Baltimore, Maryland 21218, United States ; Johns Hopkins University , Department of Mechanical Engineering, Baltimore, Maryland 21218, United States.
authors.forename: Iulian
authors.initials: I
authors.lastname: Iordachita
authors.affiliation: Johns Hopkins University , Laboratory for Computational Sensing and Robotics, Baltimore, Maryland 21218, United States ; Johns Hopkins University , Department of Computer Science, Baltimore, Maryland 21218, United States.
authors.forename: Peter
authors.initials: P
authors.lastname: Kazanzides
authors.affiliation: Johns Hopkins University , Department of Radiation Oncology, Baltimore, Maryland 21287, United States.
authors.forename: John
authors.initials: J
authors.lastname: Wong
keywords: intrafraction organ motion; mock probe; probe pressure; radiation therapy; speckle tracking; tissue deformation repeatability