A Resectoscope for Robot-Assisted Transurethral Surgery1

During transurethral resection of bladder tumor (TURBT), nonmuscle invasive bladder tumors are excised using an electrocautery wire loop or a laser fiber. The device providing transurethral access for this procedure is a resectoscope. It consists of an endoscope lens to visualize the surgery site and a working element that extends/retracts the cautery loop through an inner/outer sheath.Although TURBT is the gold standard for nonmuscle invasive bladder cancer, there remain several complications, such as bladder wall perforation, irrigant absorption (due to perforation), bleeding, and damage to ureteric orifices. These issues are generally attributed to tool and visualization limitations hindering performance [1]. Surgeons currently violate oncologic principles by removing tumors piece meal, thereby potentially contributing to tumor recurrence. There is an increasing interest in en-block resection to improve outcomes.Robotic assistance can improve bladder cancer diagnosis or treatment by offering more dexterity and workspace coverage and by supporting the deployment of novel instrumentation and imaging technologies. Most robotic assistance systems have been targeted for prostate resection or surveillance. Among the few transurethral robotic systems for bladder application, Yoon et al. reported an automated shape-memory alloy actuated mechanism for bladder cancer detection or surveillance of the bladder [2]. Using this mechanism to steer a scanning fiber endoscope, Soper et al. proposed algorithms to stitch endoscopic images of bladder offline for postoperative review [3].Goldman et al. developed a proof-of-concept telerobotic system for TURBT [4]. A multibackbone continuum robot with three working channels to pass a surgical tool, a fiberscope, and a laser fiber was deployed through an external sheath of a resectoscope in an ex vivo bovine bladder and presented successful dexterous maneuvers in reaching all the bladder zones and performing laser ablation [5]. The design was meant as a proof-of-concept for validating intravesicular dexterity but lacked critical functions for eventual clinical deployment. These missing functions are incorporated in the design presented in this paper. First, the new design adds a custom resectoscope that can be deployed transurethrally similar to a conventional resectoscope. This resectoscope would guide the continuum robot into the bladder cavity while supporting functions of visualization and irrigation. Finally, the design supports a controllable intravesicular visualization in addition to the visualization offered through the steerable robot as described in Ref. [4]. These requirements demand a new design for a robot-compatible resectoscope.We present the mechanical design of a custom resectoscope prototype that was fabricated in-house. This resectoscope has a stem at its distal section that provides working channels for a flexible tool/robot, visualization module, and irrigation. A flexible robot/tool and an endoscope can be inserted through two working channels. The resectoscope can be readily integrated into a robotic platform by sliding it onto a guide rail.Figure 1 presents a prototype of the robot-integrable resectoscope. It is approximately 18.2 in. long, 5.1 in. wide, and weighs about 980 g (without visualization equipment). The design includes a stem (1) that mainly constitutes a custom central stem housed and sealed within an external sheath (see Fig. 2), a sealed adaptor (2) which enables insertion of a visualization module and a flexible robot/tool, a 26Fr endoscope (MEDIT, Inc., Winnipeg, Canada) along with its portable light source for visualization (3), a CCD camera (KARL STORZ, Tuttlingen, Germany) (4) that couples with the endoscope through a C-clamp connection for displaying endoscopic view on a monitor, a fully rotatable endoscope guidance unit (5) to allow quick attachment and 360 deg rotation of the endoscope, an array of valves (6) for enabling controlled irrigation and selective sealing of the visualization and the tool/robot access ports, a quick-release L-shaped bracket (7) for attaching and fixing the resectoscope assembly to a rail or a linear bearing, and a camera fixture (8) that is connected to the quick-release bracket and helps carry the weight of the camera and the endoscope. The camera is gripped by twisting a knob that in turn rotates a twin lead screw. The entire camera fixture is 3D printed.Figure 2 (top) shows the stem that serves as a replacement for a traditional resectoscope access channel for manual tools. This stem is designed to provide the necessary clinical functions including delivery of inlet/outlet irrigation, light/imaging, and a working channel for flexible tool/robot delivery as shown in the bottom figure. It is composed of the central stem (1), external sheath (2), stem adaptor (3), and standard inlet/outlet Luer-lock valves (4). The central stem went through several design revisions to address economical manufacturability and sufficient irrigation flow rate. Calculations were done to determine proper irrigation channel shape and size based on fluid head loss in the channel and a minimum required flow rate of 0.6 L/min. The visualization and the tool working channels are 3 mm and 5.1 mm in diameter, respectively. The external sheath is 197 mm in length and is a standard brass alloy 260 tube having internal and external diameters of 0.351 in. and 3/8 in., respectively. A 3D-printed stem adaptor attaches the stem to an aluminum block. This block is aligned with and attached to the resectoscope adaptor distal end by dowel pins and screws.The resectoscope sealed adaptor is central to the resectoscope design. Its purpose is to ensure convenient access into the working channels of the resectoscope. These access entries include tool/robot entry at proximal end through a valve (bottom far right in Fig. 1(b)) and the visualization entry through the stopcock valve in the endoscope guidance unit. The sealed adaptor comprises two joining halves fabricated out of Delrin Acetal resin by a computer numerical controlled milling machine. Front and back aluminum attachments match and connect the adaptor with the stem and the endoscope guidance unit, respectively. A unique feature of the adaptor is that it can be rapidly opened hence facilitating access to the deployed instruments. This is a safety measure facilitating rapid tool extraction in case of system failure. In order to fulfill this requirement, several hinged stand-offs and wingnut duos are used to join bottom and top adaptor halves. In addition, all the screws connecting other parts to the adaptor are placed only in the bottom half. Calculations are performed with respect to the location of screws to prevent thread tooth stripping of plastic inserts that are used to secure the screws in the adaptor. The design of the adaptor guarantees complete sealing by O-rings and an O-ring chord placed at carefully selected locations.The resectoscope can be mounted/dismounted quickly on/from a rail or a linear bearing through a 3D-printed attachment at the bottom of quick-release bracket at the proximal end. A 1/32 in.-thick slick strip with low coefficient of friction and high abrasion-resistance (ultrahigh molecular weight polystyrene adhesive tape) is attached to the bottom to facilitate sliding action.The 3 mm endoscope could be easily inserted through the guidance unit and resectoscope adaptor channel. The flexible tool/robot deployment feasibility was also verified by successful insertion of a 5 mm continuous robot manually through the resectoscope dedicated channel (see Fig. 2 bottom). Easy and quick integration into a linear slide was verified. An experienced urologist assessed and ascertained the suitability of the prototype in terms of ease of handling/deployment, size, and weight.A novel robot-integrable resectoscope design is presented in this paper. The resectoscope is deployed in the same manner as a conventional resectoscope and thus does not alter the workflow for TURBT procedure. The resectoscope can be conveniently and quickly integrated by a sliding connection at its proximal bottom. It can be incorporated into transurethral robotic systems that aim to provide intracavity dexterity and high-quality visualization simultaneously. in vivo animal evaluation of the device remains as future work.This research was supported by the NIH Grant No. 1R21EB015623.

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