In vivo reproducibility of robotic probe placement for a novel ultrasound-guided radiation therapy system

Abstract

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.

Cooperative Control with Ultrasound Guidance for Radiation Therapy

“…The workflow is separated into a planning day, where the planning images of the patient are acquired, and multiple (fractionated) treatment days, where the radiation therapy is delivered. A more detailed discussion of this workflow can be found in Bell et al (2014) and Sen et al (2015). In this section, we focus on the use of cooperative control within this workflow.…”

“…A phantom study is performed to demonstrate that this strategy enables an operator to quickly and accurately reproduce a reference US image. As the phantom does not exhibit realistic soft-tissue deformation, an illustration of this phenomenon can be found in the in vivo canine study reported in Bell et al (2014). Much of the material presented in this paper is based on the dissertation by Sen (2016).…”

System integration and preliminary in-vivo experiments of a robot for ultrasound guidance and monitoring during radiotherapy

“…Nevertheless, two major deficiencies have become apparent when CBCT is applied to verify radiotherapy: (1) CBCT only provides a snapshot of patient information at the time of imaging, but not during actual radiation delivery, and (2) CBCT often does not provide sufficient contrast to discriminate soft tissue targets. US imaging can overcome these deficiencies as in [1]–[3], but the ionizing radiation precludes an ultrasonographer from holding the US probe on the patient during treatment. This has motivated the development of passive probe holders [4] and at least one telerobotic system [5], [6] for US monitoring during radiotherapy.…”

A Technical Note: Inter-Observer and Inter-Modality Variability of Cone-Beam Computed Tomography (CBCT) and Ultrasound (US) in Stereotactic Body Radiotherapy for Kidney Cancer

“…Lediju et al extended the use of a robotic US probe for lower abdomen in an animal study and reported that the average 3D reproducibility of their robotic US probe was less than 2 mm [17]. Moreover, the feasibility of implementing US imaging into liver SBRT for eleven patients was shown by Gurp [18].…”