This paper describes a perineal access tool for MRI-guided prostate interventions and evaluates it using a phantom study. The development of this device has been driven by the clinical need and a close collaboration effort. The device seamlessly fits into the workflow of MRI-guided prostate procedures such as cryoablation and biopsies. It promises a significant cut in the procedure time, accurate needle placement, lower number of insertions, and a potential for better patient outcomes. The current embodiment includes a frame which is placed next to the perineum and incorporates both visual and MRI-visible markers. These markers are automatically detected both in MRI and by a pair of stereo cameras (optical head) allowing for automatic optical registration. The optical head illuminates the procedure area and can track instruments and ultrasound probes. The frame has a window to access the perineum. Multiple swappable grids may be placed in this window depending on the application. It is also possible to entirely remove the grid for freehand procedures. All the components are designed to be used inside the MRI suite. To test this system, we built a custom phantom with MRI visible targets and planned 21 needle insertions with three grid types using the SCENERGY software. With an average insertion depth of about 85 mm, the average error of needle tip placement was 2.74 mm. We estimated the error by manually segmenting the needle tip in post-insertion MRIs of the phantom and comparing that to the plan.
Introduction: Biochemical recurrence of prostate cancer after definitive therapy with radical prostatectomy (RP) is
known to occur between 25-30%. We present the first known case of 1.5T MRI guided ablation using laser interstitial
thermal therapy (LITT) for locally recurrent prostate cancer following RP.
Methods: The patient elected to undergo MRI-guided LITT of the biopsy proven cancer recurrence using an FDAapproved
MRI compatible, 980nm, 15-watt laser system with MR thermometry. Under T2-weighted MR(1.5T Siemens)
imaging, guidance and targeting of the lesions with trans-perineal placement of laser applicators. Multiple cycles of laser
energy were used to ablate the tumor. A MRI-compatible urethral cooling catheter was placed to prevent urethral
thermal damage.
Results: Intra-procedural temperature mapping allowed continuous monitoring of the ablation zone and permitted
ablation control until tumor coverage was achieved. Additionally, the protective cooling effects of the urethral cooling
catheter could also be seen with the temperature mapping. Post-ablation gadolinium and T2 weighted MR imaging
demonstrated an ablation defect encompassing the recurrent tumor with no residual hyper-enhancing nodules. Three
month follow-up shows no residual or recurrent tumor seen on MR imaging.
Conclusion: This represents the first known, successful, MRI-guided, LITT procedures at 1.5T for locally recurrent
prostate adenocarcinoma following RP.
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