Accuracy of Frameless Optical Navigation in Stereotactic Laser Interstitial Thermal Therapy

Background

Glioblastoma is a rapidly growing and invasive brain tumor, and traditional treatment methods include surgical resection, radiation therapy, and chemotherapy. However, for some patients with deep-seated tumors or poor physical conditions, traditional surgical approaches pose higher risks. To address this issue, researchers have developed a novel treatment method called stereotactic laser interstitial thermal therapy (LITT). This therapy utilizes a laser probe, guided by stereotactic navigation and real-time MRI thermal monitoring, to precisely ablate tumor tissue while avoiding damage to surrounding brain tissue. Studies have shown that, similar to the extent of surgical resection, the larger the ablation volume achieved by LITT, the better the treatment outcome. Therefore, accurate placement of the laser fiber is crucial for ensuring maximum ablation of the target lesion and minimizing unnecessary tissue damage.

Research Source

This paper was written by Ilaria Viozzi, Maxime J. P. Schoonbrood, Vincent J. Ribbens, Mark ter Laan, and Christiaan G. Overduin, who are affiliated with the Radboud University Medical Center in Nijmegen, the Netherlands, and the University of Twente in Enschede, the Netherlands. The article was published on May 31, 2024, in the Journal of Neurosurgery, titled “Phantom and in vivo accuracy of frameless optical navigation in stereotactic laser interstitial thermal therapy.”

Research Content

Research Objectives

The main objectives of this research were to evaluate the accuracy of frameless stereotactic LITT probe placement using the Varioguide system, specifically:

1. Assess the accuracy of the Varioguide system in a phantom skull model.
2. Evaluate the accuracy of the Varioguide system in a clinical setting and the impact of target deviation on the maximum achievable ablation volume.

Research Methods

Phantom Experiments

The researchers used a 3D-printed polylactic acid skull phantom based on real patient CT scan data, filled with 4% agarose to simulate brain tissue. Trajectory planning was performed using electroencephalogram navigation MRI, and 24 trajectories were tested at angles of 45° and 90°, with lengths of 4 cm and 10 cm.

Seven skin markers were placed on each phantom skull for pre-operative MRI imaging and intraoperative registration. The Varioguide system was used to place the LITT cooling catheter, aiming for trajectories as close as possible to the planned trajectories. Subsequently, pilot holes were drilled, and the laser catheter was inserted, followed by intraoperative MRI imaging to record the catheter position.

Clinical Data

In the clinical setting, MRI and trajectory planning data from 10 patients participating in the EMITT pilot study were used, involving a total of 16 laser probe trajectories. All patients provided informed consent for their data to be recorded. The trajectory planning and catheter placement process followed a similar workflow as the phantom experiments, and ablation was performed under intraoperative MRI after successful catheter placement.

Data Analysis

The researchers used Matlab and SPSS for statistical analysis, quantifying the accuracy of the planned and actual trajectories using multiple parameters, such as target point error, depth deviation, lateral deviation, and angular deviation.

Main Results

Phantom Experiments

The data showed a median target point error (TPE) of 3.3 mm and an angular deviation (AD) of 1.9° in the phantom experiments. Longer trajectories (10 cm) and lower angles (45°) resulted in significantly reduced accuracy.

Clinical Experiments

In actual patients, the median target point error was 4.0 mm, and the angular deviation was 3.2°. Target deviation led to a median reduction of 6% in the maximum achievable ablation volume.

Conclusions and Significance

The study results indicate that, when using the Varioguide system for LITT probe placement, the average target error is approximately 4 mm, with shorter and straighter trajectories being more accurate. In the clinical setting, target deviation resulted in a median reduction of 6% in the planned ablation volume. These factors should be considered in LITT case planning and patient selection.

The research also emphasizes that even highly accurate frameless systems may exhibit significant inaccuracies in certain situations, which is particularly important for small target lesions or ablations near normal brain tissue. Therefore, in cases requiring higher accuracy, bone fiducial markers or frame-based systems should be considered.

Research Highlights

1. The study is the first to validate the trajectory accuracy of the Varioguide system in frameless stereotactic LITT using both phantom and clinical data.
2. The research quantified the impact of target deviation on the maximum achievable ablation volume, providing important clinical reference.

Research Limitations

The sample size was relatively small, and the results should be considered preliminary data. Additionally, the study did not include comparisons with other frameless or frame-based navigation techniques, which should be explored in future research to determine the appropriate application scenarios.

This research provides new academic evidence and technical references for the application of stereotactic laser interstitial thermal therapy in the treatment of glioblastoma, laying the foundation for future clinical practice and research.