Automated Needle Targeting (ANT) Device-Assisted Renal Access during Percutaneous Nephrolithotripsy (PCNL) Puncture: A Pilot Study to Assess the Safety and Ecacy of a Novel Technique

Background: To explore the use of an automated needle targeting (ANT) device as an assistive intraoperative navigation modality during PCNL for the treatment of large renal stones, with the aim of reducing surgical durations and radiation exposure. Methods: This open-label, single-surgeon clinical trial included patients with a diagnosis of renal stones for whom PCNL using the ANT device via the percutaneous access technique was indicated. Ethical approval was obtained from the UMMC ethics review board (Ref. 20118105-6740). The ANT was assembled after an initial motor calibration, and the image calibration was performed using the patient’s uoroscopic images. Subsequently, the ANT software calculated a bullseye alignment before percutaneous puncture. Accurate renal access was conrmed by the eux of urine in the Chiba biopsy needle, as well as by imaging with the C-arm intensier at different angles. The primary endpoints were the time to successful renal access (from ANT set-up to urine eux) and adverse events. Results: In all cases, successful renal access was achieved with a single attempt. The mean time to renal access was 6 minutes, 8 seconds. The mean uoroscopy duration was 101 seconds, with a mean radiation dose of 23.46 mGy. No adverse events were documented. Conclusion: The ANT device enabled successful, safe and ecient renal access for PCNL in this study. Further research is needed to justify the effectiveness of this device in terms of enabling accurate renal access while reducing the surgical duration and radiation exposure to both surgeons and patients.


Background
Percutaneous nephrolithotomy (PCNL) is currently considered the treatment of choice for staghorn calculi or large renal stones. Compared with open nephrolithotomy, PCNL is less invasive and is associated with reduced morbidity, while yielding good stone clearance. 1 However, inexperienced new surgeons may nd it di cult to master PCNL, as the achievement of an accurate initial puncture is essential to obtain renal access and achieve a successful outcome. Targeting of the renal calyx using 2d uoroscopy images for guidance can be di cult particularly in situations where the stones are lodged in the calyx of the kidney. 2 To overcome this learning curve, researchers have explored improvements in intra-operative imaging and, more recently, the introduction of intra-operative navigation systems. The Johns Hopkins University Group reported on PAKY-RCM, a joystick-driven system that uses a robotic arm to support a puncture needle and direct its insertion. 3 In 2011, Cinquin et al. reported a similar system wherein the robotic arm functioned as an adjunct to compliment the surgeon's movement during renal access. 4 The automated needle targeting (ANT) device is a software-controlled automated electromechanical robot arm. This device was developed to provide needle guidance and stabilization for surgeons during the establishment of renal access for PCNL. The aim of the device is to reduce the time required to establish accurate renal access and thus minimize the exposure of surgeons, theatre personnel and the patient to radiation. 5 The ANT device-assisted technique couples intra-operative uoroscopic imaging with image registration software, which uses a closed-loop feedback system to align the puncture needle to the desired calyx prior to the actual puncture. The ANT robot is mainly composed of medical-grade polyether ether ketone (PEEK), and is constructed from three main components: the robot, motor controller box and the articulated arm (Fig. 1). 5 In this report, we describe our initial experience with the ANT device and the associated safety and e cacy during the establishment of the initial puncture and renal access for PCNL.

Methods
This was a phase one rst-in-man, open-label, non-randomized, parallel-design safety and e cacy study of subjects who underwent PCNL with ANT device-assisted renal access. Ethical approval for the study was This pilot study included ve patients at the UMMC in Kuala Lumpur who were diagnosed with renal calculi within a 3-month period and for whom prone PCNL with ANT device-assisted renal access was indicated. The inclusion criteria were age older than 18 years, informed consent to participate, renal calculi larger than 1 cm and no history of treatment for renal calculi. Patients who had previously received extracorporeal shockwave lithotripsy (ESWL) or ureterorenoscopy were excluded. The clinical decision to undergo PCNL instead of another treatment modality (such as retrograde intrarenal surgery, ESWL) depended entirely on the clinical indication according to existing guidelines and the standard of care. In this study, all PCNL procedures were performed by a single consultant urologist.

Endpoints
The primary endpoints for this study were a successful needle puncture that enabled the surgeon to proceed to dilatation and stone fragmentation and extraction, as well as the assessment of any adverse events arising from the use of the ANT device. The following parameters were assessed: needle insertion time, time to target, total time for puncture, number of needle insertion attempts to obtain access and total radiation dosage (measured from placement of the robot until the e ux of urine). The needle insertion time was measured from the mounting of the ANT device until the e ux of urine during successful renal access. The time to target was de ned as the time from the targeting of the needle on the skin to successful needle targeting via software and uoroscopy image coordination. The total time for puncture was de ned as the time from identi cation of the calyx to the e ux of urine via successful needle puncture.

Preoperative Preparation and Positioning
In accordance with the standard protocol for prone PCNL at our center, all patients were rst placed in the lithotomy position. A ureteric catheter was inserted, and its placement was con rmed via uoroscopy.
Subsequently, the patient was turned to the prone position and sterilized and draped according to the standard PCNL procedure. The ANT device was then assembled and mounted to the operating table as shown in Fig. 2. The device was positioned between the C-arm and the patient and aligned with the renal stone in a sterile manner (Fig. 2). The target calyx for renal access was chosen according to the surgeon's clinical judgement and preference.

ANT-assisted Renal Access
Once positioned, motor calibration of the ANT device was performed by coupling the intraoperative uoroscopy images with the ANT software (Fig. 3). The puncture needle within the needle sheath was placed in the articulated arm of the device. The ANT software performed an oriented calculation to achieve a bullseye alignment and optimal trajectory. To overcome renal mobility with breathing, respiration was stopped during renal access with the ANT device. The surgeon then performed the PCNL puncture by advancing the needle within the sheath into the renal calyx. With assistance from the anaesthetist, respiration was resumed once needle alignment and puncture was done. Accurate renal access was con rmed by the e ux of urine into the needle sheath, as well as by imaging with the C-arm positioned at variable angles. A guide wire was then passed into the renal collecting system before the ANT device was disassembled and removed from the operating table. Subsequently, the standard PCNL procedure, which comprised access tract dilatation followed by stone fragmentation and complete extraction, was performed.

Results
All the 5 cases in this pilot study required only a single puncture to achieve successful renal access ( Table 1). The mean needle insertion time was 6 minutes and 8 seconds, the mean time to target was 3.8 minutes and the mean total time for puncture was 8.18 minutes. The mean duration of radiation exposure during placement of the ANT device was 1.41 minutes, which corresponded to a dose of 23.46 mGy (Table 1). No adverse events were documented.

Discussion
In this pilot study, we are successful in executing the concept of the ANT device and its safety in establishment of the initial puncture and renal access for PCNL.
Learning Curve PCNL is currently the standard of care for large renal stones (> 2 cm) and can achieve a good stone-free rate. However, this technique remains challenging to master, 1 as evidenced by the increased morbidity associated with the procedure, especially when performed by an inexperienced urological surgeon. 6 It has been reported that a new urologist could achieve surgical competence in PCNL after performing 40-60 procedures, including the mastery of all key steps such as calyceal puncture, track dilatation, endoscopic manipulation, lithotripsy and nephrostomy insertion. 2 Based on our ndings, we contend that the ANT device could assist new surgeons with this learning curve by improving the calyceal puncture step. The ANT device uses a bullseye technique to achieve renal access, and surgeons can use this tool as a guide to orientate and advance the puncture needle into the renal calyx. In a future study ANT-assisted renal access should be compared with conventional free-hand puncture.

Renal Access
The common major complications (Clavien-Dindo grade > III) of PCNL are associated with percutaneous puncture during renal access, and may include injury to the adjacent organs, violation of the pleural space, bleeding or infection. 7 In our cohort of patients, renal access was completed successfully with a single needle puncture attempt in all cases. This result suggests that the ANT device may help to reduce the risk of renal access-related complications caused by the number of puncture attempts. In the future, insu cient experience may no longer be a major cause of complications associated with PCNL. Moreover, the reduced number of puncture attempts will help to reduce the total procedural duration.

Radiation Exposure
In a previous report, Bohdan et al. reported an average uoroscopy time during PCNL of approximately 175 seconds. 8 Moreover, Allen et al. reported that the uoroscopy time and radiation dose only reached plateaus after 115 cases. 9 In our cohort, the mean uoroscopy time was 101 seconds. A reduced uoroscopy time and consequently decreased radiation exposure would bene t not only the patient but also the surgeon, particularly as the cumulative radiation dose would increase with an increasing number of cases. Furthermore, the ANT device removes the need for the surgeon's hand to be in close proximity of radiation area during bullseye alignment and therefore reduces risk of radiation exposure. One might argue that the use of ultrasound-guided renal access during the PCNL procedure could also signi cantly minimize the radiation exposure. However, ultrasound imaging is operator-dependent, and successful renal access under the guidance of this modality would require the mastery of a completely different learning curve. Furthermore, intra-operative ultrasound devices are not readily available at all centers.

Robotic-assisted PCNL devices
Since the rst introduction of "robotic"-assisted PCNL in 2009, 1 the common limitations faced by users have included di culty with the initial set-up, the absence of tactile feedback from the robot and di culty with sterilization of the robot. The ANT device was developed to address these disadvantages. Similar to a self-retaining retractor, the ANT device can be easily mounted to the operative eld using a clip and screw-on hinge placed on the operating table. The exible working arm can be adjusted easily and focused on the operating eld. Once renal assess is successfully achieved, the ANT device can be unscrewed and removed swiftly. Moreover, the ANT device assists the surgeon in achieving an accurate bullseye allocation and placement of the puncture needle, and functions as a sheath to ensure constant and steady needle angulation during the renal access puncture. This design thus preserves tactile feedback during the performance of a renal access puncture, which may be especially useful as it allows the surgeon to feel the "give" during renal access and thus avoid the risk of injury to the surrounding structures. Finally, the ANT device is autoclavable, which facilitates device sterilization and thus effectively prevents the transmission of device-related infectious diseases.

Limitations
This was a pilot study to assess the safety and e cacy of the ANT device. Therefore, we did not attempt to achieve renal access in complex scenarios, such as patients with full staghorn calculi, a nonhydronephrotic kidney or a complex renal anatomy. A future study involving a larger cohort and a control group will better enable us to assess the role of the ANT device in such di cult cases. Moreover, we did not test the ANT device during the performance of renal access in the supine position. This may also be a subject of future research. It came to our attention that ceasing respiration is important to assist in accurate renal access using the ANT device. Moving forward, future research and developments can look into negating this by syncing the ANT device with movements caused by respiration. As this is a phase one study with the ANT device, a variance in the targeting time could also be due to the surgeon familiarizing with the device.

Conclusion
Our pilot study demonstrates the promising capability of the ANT device to enable successful, safe and e cient renal access for PCNL. Further studies are needed to justify the e cacy and accuracy of this device for the achievement of renal access while reducing surgical duration and radiation exposure to both surgeons and patients.

Availability of data and materials
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Figure 1
The automated needle targeting device comprises 3 main parts: the articulated arm, motor controller box and robot.