Peter Guion

Initial clinical experience with real‐time transrectal ultrasonography‐magnetic resonance imaging fusion‐guided prostate biopsy

To evaluate the feasibility and utility of registration and fusion of real‐time transrectal ultrasonography (TRUS) and previously acquired magnetic resonance imaging (MRI) to guide prostate biopsies.

Simultaneous integrated boost of biopsy proven, MRI defined dominant intra-prostatic lesions to 95 Gray with IMRT: early results of a phase I NCI study

BackgroundTo assess the feasibility and early toxicity of selective, IMRT-based dose escalation (simultaneous integrated boost) to biopsy proven dominant intra-prostatic lesions visible on MRI.MethodsPatients with localized prostate cancer and an abnormality within the prostate on endorectal coil MRI were eligible. All patients underwent a MRI-guided transrectal biopsy at the location of the MRI abnormality. Gold fiducial markers were also placed. Several days later patients underwent another MRI scan for fusion with the treatment planning CT scan. This fused MRI scan was used to delineate the region of the biopsy proven intra-prostatic lesion. A 3 mm expansion was performed on the intra-prostatic lesions, defined as a separate volume within the prostate. The lesion + 3 mm and the remainder of the prostate + 7 mm received 94.5/75.6 Gray (Gy) respectively in 42 fractions. Daily seed position was verified to be within 3 mm.ResultsThree patients were treated. Follow-up was 18, 6, and 3 months respectively. Two patients had a single intra-prostatic lesion. One patient had 2 intra-prostatic lesions. All four intra-prostatic lesions, with margin, were successfully targeted and treated to 94.5 Gy. Two patients experienced acute RTOG grade 2 genitourinary (GU) toxicity. One had grade 1 gastrointestinal (GI) toxicity. All symptoms completely resolved by 3 months. One patient had no acute toxicity.ConclusionThese early results demonstrate the feasibility of using IMRT for simultaneous integrated boost to biopsy proven dominant intra-prostatic lesions visible on MRI. The treatment was well tolerated.

An MRI-Compatible Robotic System With Hybrid Tracking for MRI-Guided Prostate Intervention

This paper reports the development, evaluation, and first clinical trials of the access to the prostate tissue (APT) II system-a scanner independent system for magnetic resonance imaging (MRI)-guided transrectal prostate interventions. The system utilizes novel manipulator mechanics employing a steerable needle channel and a novel six degree-of-freedom hybrid tracking method, comprising passive fiducial tracking for initial registration and subsequent incremental motion measurements. Targeting accuracy of the system in prostate phantom experiments and two clinical human-subject procedures is shown to compare favorably with existing systems using passive and active tracking methods. The portable design of the APT II system, using only standard MRI image sequences and minimal custom scanner interfacing, allows the system to be easily used on different MRI scanners.

Closed-loop control in fused MR-TRUS image-guided prostate biopsy

Multi-modality fusion imaging for targeted prostate biopsy is difficult because of prostate motion during the biopsy procedure. A closed-loop control mechanism is proposed to improve the efficacy and safety of the biopsy procedure, which uses real-time ultrasound and spatial tracking as feedback to adjust the registration between a preoperative 3D image (e.g. MRI) and real-time ultrasound images. The spatial tracking data is used to initialize the image-based registration between intraoperative ultrasound images and a preoperative ultrasound volume. The preoperative ultrasound volume is obtained using a 2D sweep and manually registered to the MRI dataset before the biopsy procedure. The accuracy of the system is 2.3 +/- 0.9 mm in phantom studies. The results of twelve patient studies show that prostate motion can be effectively compensated using closed-loop control.

Development and Evaluation of an Actuated MRI-Compatible Robotic System for MRI-Guided Prostate Intervention

This paper reports the design, development, and magnetic resonance imaging (MRI) compatibility evaluation of an actuated transrectal prostate robot for MRI-guided needle intervention in the prostate. The robot performs actuated needle MRI guidance with the goals of providing 1) MRI compatibility; 2) MRI-guided needle placement with accuracy sufficient for targeting clinically significant prostate cancer foci; 3) reducing interventional procedure times (thus increasing patient comfort and reducing opportunity for needle targeting error due to patient motion); 4) enabling real-time MRI monitoring of interventional procedures; and 5) reducing the opportunities for error that arise in manually actuated needle placement. The design of the robot, employing piezoceramic-motor actuated needle guide positioning and manual needle insertion, is reported. Results of an MRI compatibility study show no reduction of MRI signal-to-noise ratio (SNR) with the disabled motors. Enabling the motors reduces the SNR by 80% without radio frequency (RF) shielding, but the SNR is only reduced by 40-60% with RF shielding. The addition of RF shielding is shown to significantly reduce image SNR degradation caused by the presence of the robotic device. An accuracy study of MRI-guided biopsy needle placements in a prostate phantom is reported. The study shows an average in-plane targeting error of 2.4 mm with a maximum error of 3.7 mm. These data indicate that the systems needle targeting accuracy is similar to that obtained with a previously reported manually actuated system, and is sufficient to reliably sample clinically significant prostate cancer foci under MRI guidance.

Patient selection determines the prostate cancer yield of dynamic contrast‐enhanced magnetic resonance imaging‐guided transrectal biopsies in a closed 3‐Tesla scanner

To evaluate the cancer yield of transrectal prostate biopsies in a 3‐T magnetic resonance imaging (MRI) scanner in patients with elevated prostate specific antigen (PSA) levels and recent negative transrectal ultrasonography (TRUS)‐guided prostate biopsies.

MRI-guided robotic prostate biopsy: a clinical accuracy validation

UNLABELLED Prostate cancer is a major health threat for men. For over five years, the U.S. National Cancer Institute has performed prostate biopsies with a magnetic resonance imaging (MRI)-guided robotic system. PURPOSE A retrospective evaluation methodology and analysis of the clinical accuracy of this system is reported. METHODS Using the pre and post-needle insertion image volumes, a registration algorithm that contains a two-step rigid registration followed by a deformable refinement was developed to capture prostate dislocation during the procedure. The method was validated by using three-dimensional contour overlays of the segmented prostates and the registrations were accurate up to 2 mm. RESULTS It was found that tissue deformation was less of a factor than organ displacement. Out of the 82 biopsies from 21 patients, the mean target displacement, needle placement error, and clinical biopsy error was 5.9 mm, 2.3 mm, and 4 mm, respectively. CONCLUSION The results suggest that motion compensation for organ displacement should be used to improve targeting accuracy.

Intra- and inter-radiation therapist reproducibility of daily isocenter verification using prostatic fiducial markers

BackgroundWe sought to determine the intra- and inter-radiation therapist reproducibility of a previously established matching technique for daily verification and correction of isocenter position relative to intraprostatic fiducial markers (FM).Materials and methodsWith the patient in the treatment position, anterior-posterior and left lateral electronic images are acquired on an amorphous silicon flat panel electronic portal imaging device. After each portal image is acquired, the therapist manually translates and aligns the fiducial markers in the image to the marker contours on the digitally reconstructed radiograph. The distances between the planned and actual isocenter location is displayed. In order to determine the reproducibility of this technique, four therapists repeated and recorded this operation two separate times on 20 previously acquired portal image datasets from two patients. The data were analyzed to obtain the mean variability in the distances measured between and within observers.ResultsThe mean and median intra-observer variability ranged from 0.4 to 0.7 mm and 0.3 to 0.6 mm respectively with a standard deviation of 0.4 to 1.0 mm. Inter-observer results were similar with a mean variability of 0.9 mm, a median of 0.6 mm, and a standard deviation of 0.7 mm. When using a 5 mm threshold, only 0.5% of treatments will undergo a table shift due to intra or inter-observer error, increasing to an error rate of 2.4% if this threshold were reduced to 3 mm.ConclusionWe have found high reproducibility with a previously established method for daily verification and correction of isocenter position relative to prostatic fiducial markers using electronic portal imaging.

Development and preliminary evaluation of an actuated MRI-compatible robotic device for MRI-guided prostate intervention

This paper reports the design, development, and magnetic resonance imaging (MRI) compatibility evaluation of an actuated transrectal prostate robot for MRI-guided intervention. The robot employs an actuated needle guide with the goal of reducing interventional procedure times and increasing needle placement accuracy. The design of the robot, employing piezo-ceramic-motor actuated needle guide positioning and manual needle insertion, is reported. Results of a MRI compatibility study show no reduction of MRI image signal-to-noise-ratio (SNR) with the motors disabled and a 40% to 60% reduction in SNR with the motors enabled. The addition of radio-frequency (RF) shielding is shown to significantly reduce image SNR degradation due to the presence of the robotic device.

Fusion of real-time transrectal ultrasound with pre-acquired MRI for multi-modality prostate imaging

A system for fusion of realtime transrectal ultrasound (TRUS) with pre-acquired 3D images of the prostate was designed and demonstrated in phantoms and volunteer patients. Biopsy guides for endocavity ultrasound transducers were equipped with customized 6 degree-of-freedom (DoF) electromagnetic (EM) tracking sensors, compatible with the Aurora EM tracking system (Northern Digital Inc, NDI, Waterloo, ON, Canada). The biopsy guides were attached to an ultrasound probe and calibrated to map tracking coordinates with ultrasound image coordinates. Six cylindrical gold seeds were placed in a prostate phantom to serve as fiducial markers. The fiducials were first identified manually in 3T magnetic resonance (MR) images collected with an endorectal coil. The phantom was then imaged with tracked realtime TRUS and the fiducial markers were identified in the live image using custom software. Rigid registrations between MR and ultrasound image space were computed and evaluated using subsets of the fiducial markers. Twelve patients were scanned with 3T MRI and TRUS for biopsy and seed placement. In ten patients, volumetric ultrasound images were reconstructed from 2D sweeps of the prostate and were manually registered with the MR. The rigid registrations were used to display live TRUS images fused with spatially corresponding realtime multiplanar reconstructions (MPRs) of the MR image volume. Registration accuracy was evaluated by segmenting the prostate in the MR and volumetric ultrasound and computing distance measures between the two segmentations. In the phantom experiments, registration accuracies of 2.2 to 2.3 mm were achieved. In the patient studies, the average root mean square distance between the MR and TRUS segmentations was 3.1 mm, the average Hausdorff distance was 9.8 mm. Deformation of the prostate during MR and TRUS scan was identified as the primary source of error. Realtime MR/TRUS image fusion is feasible and is a promising approach to improved target visualization during TRUS-guided biopsy or therapy procedures.