**4. Computer-assisted needle guidance**

Computer-assisted surgery (also known as stereotactic surgery) is established in fields like orthopedics and neurosurgery and emerged from "being just around the corner" to clinical routine of abdominal surgery over the recent decade [33]. When it comes to needle guidance, Beerman et al. [34] have reported the experiences from 1000 consecutive cases using computer-assisted image-guidance in liver ablations. The key message of this study is the necessity of navigation solutions with respect to reproducibility in percutaneous, laparoscopic, and open interventions [34]. Another report investigating the accuracy between guided and manual probe placement shows a significant advantage for the guided approach [35]. Martin et al. [36] discuss the advantages of computer assistance in the placement of single needles during a liver phantom study demonstrating that 95% of the participants were able to hit the center of the tumor using the computer-assisted approach compared to 65% with ultrasound (US) only.

The system used in the above studies was designed by CAScination (Bern, Switzerland) and provides guidance for interventional and surgical liver procedures (see **Figure 3**).

With regard to minimally invasive applications the system discriminates between the percutaneous and laparoscopic approach in the following aspects:

#### **4.1 Percutaneous ablation**

The navigation system supports the clinician during percutaneous ablation, which is performed in the intervention suite using computed tomography (CT) or conebeam CT (CBCT) imaging. The patient is under general anesthesia with respiratory motion control and positioned on a vacuum mattress. Retroreflective single markers are attached to the patient's skin using a dedicated marker template. The single markers are detectable by the optical tracking camera and in the tomographic images and build the foundation for virtual to physical space registration. Furthermore, their spatial position is used for monitoring of patient movement throughout the procedure. The needle trajectories are then planned, navigated, and verified using CT images, with the possibility of planning IRE needle configurations (**Figure 4**).

#### **Figure 3.**

*Setup for percutaneous needle insertion. Aiming device (A), touch monitors (B), optical tracking camera (C), patient markers (D).*

#### **Figure 4.**

*Percutaneous workflow from left to right: Patient marker attachment, CT-based IRE trajectory planning, positioning of aiming device, and needle placement control.*

For the initial planning image, contrast-enhanced CT is the preferred choice to achieve a good discrimination between the structures of interest. To further enhance the planning procedure, a preoperative MRI image can be fused with the intraoperative image data to visualize structures not traceable in the intraoperative CT.

Lachenmayer et al. [37] retrospectively analyzed the system in 174 percutaneous ablations of hepatocellular carcinoma (HCC) and reported a median lateral error of 3.2 (0.2–14.1) mm. They concluded that percutaneous, computer-assisted needle navigation is safe and efficient for treatment of HCC. Beyer et al. [38, 39] evaluated the system against manual, CT-fluoroscopically guided probe placement for IRE of liver tumors. The CAScination guidance (n = 10) was compared against manual guidance (n = 10) and they reported a significant decrease in planning time (55 vs. 104 min, P < 0.001) and radiation exposure. The procedural accuracy, measured as the deviation of the IRE electrodes with respect to a defined reference electrode, was significantly higher for the navigated approach (2.2 vs. 3.3 mm mean deviation, P < 0.001) [39].

*Computer Assistance in the Minimally Invasive Ablation Treatment of Pancreatic Cancer DOI: http://dx.doi.org/10.5772/intechopen.93226*

### **4.2 Laparoscopic ablation**

The system for laparoscopic needle navigation relies on a surface landmark registration in which distinct points on the organ surface are sampled with tracked instruments and matched with the corresponding points from available patient image data. These data include preoperative CT images with optional 3D reconstructions from structures of interest. Guidance is achieved by tracking of the ablation needle using retroreflective markers attached to the hand piece (**Figure 5**).

A major drawback for the surface landmark-based registration approach is organ deformation due to pneumoperitoneum, which downgrades navigation accuracy on preoperative image data. Intraoperative CT imaging would help to reduce deformation artifacts; however, this requires the availability of a hybrid OR [40]. Prevost et al. [41] investigated the laparoscopic guidance solution for liver resection and ablation in 10 cases with the main conclusion being that the navigation system enhances the explorative phase, yet the registration accuracy was not sufficient for reliable tool navigation. Stillström et al. [42] pioneered in the application of computer assistance in laparoscopic pancreas IRE. They reported the feasibility of imageguided navigation in the operating theater even though the system was mainly used for orientation purposes.

#### **4.3 Needle guidance**

The CAScination system distinguishes between two approaches for needle guidance, namely active and passive guidance. The active guidance (freehand approach) makes use of instrument calibration to determine the needle tip with respect to the marker shield attached to the hand piece of the needle, whereas passive guidance makes use of a tracked mechanical arm (aiming device approach) which is pre-calibrated due to known geometric properties. While the former provides the advantage of visualizing the needle tip during the insertion to obtain an active depth control, it is affected by errors resulting from the calibration and needle bending. The latter is not affected by the calibration error and reduces the bending artifacts by means of brackets guiding the needle along the oriented path. During needle insertion, the lateral deviation from the original plan is of high significance as it may require needle repositioning. Wallach et al. [43] compared the two approaches during a phantom study with 25 needle punctures on a nonrigid phantom. The resulting lateral error of the needle to the defined target was found to be significantly lower with the aiming device (2.3 ± 1.3 mm vs. 4.2 ± 2.0 mm) [43].

#### **Figure 5.**

*Laparoscopic workflow from left to right: preoperative image segmentation, optical instrument calibration, landmark-based registration, targeting with active depth control.*

#### **4.4 Alternative navigation solutions**

There are a number of navigation solutions for abdominal organs on the market. These devices share the same fundamental functional principles and provide a different range of functionalities, which can be used in the setting of IRE on the pancreas. Given the high accuracy requirements and the complexity in needles placement relative to a number of risk structures, we deem functionality for multineedle planning as well as accurate needle guidance as mandatory requirements for navigated IRE on the pancreas. The following paragraphs present different available navigation solutions and evaluate them with respect to these two requirements.

The IMACTIS® CT (Imactis SAS, La Tronche, France) solution is designed for percutaneous interventions using CT imaging and electromagnetic instrument tracking. The device was applied on different target organs and available literature includes an assessment of needle positioning accuracy and time requirements in a prospective randomized trial. The median Euclidean error [interquartile range] using the computer-assisted approach was found to be 4.1 mm [2.7–9.1 mm] compared to 8.9 mm [4.9–15.1 mm] for the non-navigated group for a total of 120 patients [44]. This shows that IMACTIS® CT has the potential to reach sufficient accuracy for IRE needle placement. Its shortcoming with respect to the application of pancreatic IRE lies in the fact that the device has no functionality for needle planning and multi-needle treatments.

The MAXIO (Perfint Healthcare, Florence, Oregon, USA) is used in CT-guided, percutaneous interventions and includes a robotic arm for needle placement. The device comprises a planning software supporting single- as well as multi-needle planning for different needle types. Beyer et al. [38] investigated the MAXIO with respect to procedural accuracy in a retrospective study of 40 cases of liver IRE conducted by an experienced interventional radiologist. Out of these, 19 were conducted using manual needle placement under CT fluoroscopy guidance and 21 with guidance of the robotic system. To calculate the procedural accuracy, an oblique slice was placed at the needle tip closest to the tumor with the normal pointing along the needle direction. Each needle tip was successively projected on the slice translated 3 cm from the tip toward the hand piece to calculate the distance to the needle center. The resulting accuracy was significantly improved when comparing the robotic approach to freehand needle placements (2.2 vs. 3.1 mm) [38].

The navigation system Explorer (Pathfinder) is designed for needle guidance in open liver surgery and is based on optical instrument tracking (same functional principle as CAS-One for the laparoscopic use case). A study by Bond et al. [45] investigated needle guidance accuracy and required time in a randomized controlled trial of IRE for pancreatic cancer. The application of the Explorer device decreased time for needle placement from 20 to 11 min while reaching an accuracy of 3.4 mm in relative spacing between the needles. The accuracy of needle placement with respect to the target anatomy is expected to be lower as the publication reports average fiducial registration errors of 10.8 mm. The authors conclude that the main benefit of the navigated approach is the increase of the surgeon's confidence to localize the needle using stereotactic navigation. The image to physical space registration is seen as the biggest obstacle to achieve a reliable overlay between the preoperative plan and the intraoperative scene.

Further guidance solutions for pancreatic IRE potentially include the use of ultrasound fusion devices such as those used in percutaneous ablation treatment on the liver. While providing needle guidance under real-time feedback, there are no devices providing multi-needle planning functionality together with ultrasoundbased needle navigation. To our knowledge, there are no reports on the usage of ultrasound-fusion and navigation devices in the setting of pancreatic IRE.

*Computer Assistance in the Minimally Invasive Ablation Treatment of Pancreatic Cancer DOI: http://dx.doi.org/10.5772/intechopen.93226*
