Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Doctor of Philosophy


Biomedical Engineering


Fenser, Aaron


Advances in prostate cancer (PCa) screening techniques have led to diagnosis of many cases of low-grade and highly localized disease. Conventional whole-gland therapies often result in overtreatment in such cases and debate still surrounds the optimal method of oncologic control. MRI-guided prostate focal laser ablation (FLA) is a minimally invasive treatment option, which has demonstrated potential to destroy localized lesions while sparing healthy prostatic tissue, thereby reducing treatment-related side effects. Many challenges still exist in the development of FLA, including patient selection; tumour localization, visualization, and characterization; needle guidance; and evaluation of treatment efficacy. The objective of this thesis work was to advance and enhance techniques for needle guidance in MRI-guided focal laser ablation (FLA) therapy of PCa.

Several steps were taken in achieving this goal. Firstly, we evaluated the overlap between identified lesions and MRI-confirmed ablation regions using conventional needle guidance. Non-rigid thin-plate spline registration of pre-operative and intra-operative images was performed to align lesions with ablation boundaries and quantify the degree of coverage. Complete coverage of the lesion with the ablation zone is a clinically important metric of success for FLA therapy and we found it was not achieved in many cases. Therefore, our next step was to develop an MRI-compatible, remotely actuated mechatronic system for transperineal FLA of prostate cancer. The system allows physicians in the MRI scanner control room to accurately target lesions through 4 degrees of freedom while the patient remains in the scanner bore. To maintain compatibility with the MRI environment, piezoelectric motors were used to actuate the needle guidance templates, the device was constructed from non-ferromagnetic materials, and all cables were shielded from electromagnetic interference. The MR compatibility and needle placement accuracy of the device were evaluated with virtual and phantom targets.

The system should next be validated for accuracy and usefulness in a clinical trial where more complex tissue properties and potential patient motion will be encountered. Future advances in modeling the tissue properties and compensating for deformation of the prostate, as well as predicting needle deflection, will further bolster the potential of FLA as option for the management of PCa.

Summary for Lay Audience

Prostate cancer (PCa) is the most common non-skin cancer in Canadian men, but many cases are low-grade, meaning they are unlikely to cause death. Often, the side effects of typical treatments such as surgery or radiation are worse than the symptoms of the cancer itself. Focal laser ablation (FLA) is an alternative treatment option which can be used to treat low-grade PCa with fewer side effects than traditional treatments. FLA uses needles inserted through the skin and into the prostate to heat and destroy tumours from the inside. The needles are guided using magnetic resonance images (MRI), which are created using powerful magnetic fields that can “see” inside the body. The overall goal of this work was to improve the accuracy and useability of MRI-guided FLA for PCa.

The first step was to compare ablation zones (regions of tissue destroyed by FLA) with the locations of the tumours that were to be destroyed. To do this, MRI images where the tumours were visible were aligned with images where the ablation zones were visible. In many cases, the ablation zone did not completely overlap the tumour, which meant part of the tumour may have been left untreated. Therefore, the next step was to develop a robot which could more accurately place needles for FLA.

This robot was constructed using specialized motors and materials which would not be affected by the strong magnetic fields of the MRI scanner. The robot can adjust both the angle and position of a needle before it penetrates the skin. A series of tests were done to verify the robot’s MRI-compatibility and then the accuracy with which it could place needles was measured in artificial prostate models. It was shown that the robot can place needles within 4.13 mm of an intended target 95% of the time. This is a high enough level of accuracy for FLA therapy, and it can be accomplished while the physician is outside of the MRI scanner room. The next step for the robot is to be used in clinical trials, where its safety and effectiveness can be demonstrated in real patients.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.