A system for MRI-guided transperineal delivery of needles to the prostate for focal therapy

Purpose: To demonstrate the capabilities of a new magnetic resonance imaging (MRI)-guided system for delivering needles to the prostate for focal therapy. Included is a presentation of the design of the system and its user interface, evaluation of MR-compatibility, and quantitative evaluation of guidance accuracy and repeatability within the bore of a clinical MRI scanner. Methods: The use of MRI for visualization of tumors, intraoperative visualization of interventional tools, and thermometry for controlled ablation of lesions is becoming increasingly prevalent. In this work, the authors present a prototype system for guiding needles to prostate tumors within the bore of an MRI scanner for use in focal laser thermal ablation of prostate tumors. The system consists of a manually actuated trajectory alignment device that allows a physician to precisely align a set of needle guides with an intended target in the prostate within the bore of a clinical closed-bore MRI scanner. Needle insertion is then performed transperineally, with the patient in the bore of the MRI, and custom software provides monitoring of thermal ablative procedures. Results: The system is shown to have a minimal effect on image distortion, and only a 6% decrease in image signal-to-noise ratio. Through needle insertion tests in tissue-mimicking phantoms, the system's potential for reliably guiding needles to intra-MR targets within 2.64 mm has been demonstrated. Use of the system to deliver focal laser ablation therapy to two patients showed that it can be used to deliver needles with minimal disruption of workflow, and in less time than when insertions are performed freehand or with a fixed grid template. Conclusions: A system for delivering needles to a patient's prostate for focal therapy within the bore of an MRI scanner has been developed. Results from needle insertion tests in phantoms suggest that the system has the potential to provide accurate delivery of focal therapy to prostate tumors of the smallest clinically significant size. Initial tests in two patients showed that needle deflection was larger than in phantoms, but methods of manually compensating for this effect were employed and needles were delivered to treatment sites with sufficient accuracy to deliver effective treatment. In addition, the treatment was delivered in less time than with a fixed grid template or freehand insertions. Despite this success, methods of reducing needle deflection are needed in order to fully utilize the potential of this system, and further reduce total procedure time. (C) 2013 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4773043]