robotic prostate surgeryurobotics.urology.jhu.edu/pub/2006-muntener-ermd.pdf · 2006-11-13 ·...

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Review

10.1586/17434440.3.5.575 © 2006 Future Drugs Ltd ISSN 1743-4440 575www.future-drugs.com

Robotic prostate surgeryMichael Muntener, Daniel Ursu, Alexandru Patriciu, Doru Petrisor and Dan Stoianovici†

†Author for correspondenceThe Johns Hopkins Medicine, URobotics Laboratory, Department of Urology, Mason F Lord West Tower, Room W115, 5200 Eastern Avenue, Baltimore, MD 21224, USATel.: +1 410 550 1980Fax: +1 410 550 [email protected]

KEYWORDS: computer-assisted surgery, MRI compatible, prostate, robotics

The increasing popularity of robot-assisted radical prostatectomy has put the field of robotics in the spotlight. However, the relationship between medical robotics and the field of urology is older than most urologists know and it will most likely have a bright future beyond any contemporary application. The objective of this review is to provide an insight into the fundamentals of medical robotics and to highlight the history, the present and the future of urological robotic systems with an emphasis on robotic prostate interventions.

Expert Rev. Med. Devices 3(5), 575–584 (2006)

Over the past few decades technologicaladvances have revolutionized the way wepractice medicine. Today, medicine reliesheavily on technical equipment and technol-ogy is evolving ever more rapidly. The field ofurology has a very rich tradition of embracingthe use of advanced and pioneering technol-ogy to make existing procedures more toler-able and efficient as well as developing newtreatment modalities. The advent of roboticsin prostate surgery is a new horizon of thistradition. The robot-assisted laparoscopicradical prostatectomy (LRP) is certainly arobotic success story and the da Vinci®

Surgical System (Intuitive Surgical) is themost famous representative of medical robotscurrently in use. However, the use of robotsfor prostatic interventions has a longer, lesswell-known history and it will most likelyhave a bright future beyond any currentapplication. Apart from a general overview ofrobotic surgical systems, this review will focuson the past, present and future of roboticprostate interventions.

Fundamentals of surgical roboticsThe robot, a term first coined by the Czechplaywright Karel Capek in 1921 in his playRossums Universal Robots, comes directlyfrom the Czech word ‘robot’ which meansindustrial worker. It is of no surprise then thatthe first robots, as we know them today,appeared in the fields of industrial

manufacturing where automatization becameincreasingly important for economic efficiencyduring and after World War II.

By definition, a robot is a mechanical devicethat is controlled using a computer system [1].In particular, a medical robot is a controllablemechanical device that undertakes one of fourhealthcare-specific roles: a supportive role topatient and staff, laboratory assistance, forrehabilitation or surgery. Urological medicalrobots are robots that belong to the lastcategory and are defined by three essentialcomponents: the manipulator, imageacquisition device and a computer.

The surgical manipulator is an electro-mechanical arm equipped with sensors andactuators responsible for holding and preciselymoving instruments under computer control.The most commonly employed kinematicarchitecture for surgical manipulators is theremote center of motion (RCM) concept [2],developed in 1995 at IBM®

[3]. This architec-ture, specific to surgical robots, aims to repro-duce a surgeon’s natural motion during laparo-scopic surgery by allowing the manipulator toconsistently enable and facilitate the pivotingof instruments about a fixed point in spaceduring the surgical procedure; that is, thepoint where the laparoscopic instrumententers the body (FIGURE 1) [4].

The image acquisition device allows therobot and surgeon to visualize the surgicalenvironment and define the operating tasks

CONTENTS

Fundamentals of surgical robotics

History & past achievements

Present robotic applications in prostate surgery

Future robotic applications in prostate interventions

Expert commentary & five-year view

Key issues

References

Affiliations

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Muntener, Ursu, Patriciu, Petrisor & Stoianovici

576 Expert Rev. Med. Devices 3(5), (2006)

of the robot. Different imaging modalities, such as MRI,ultrasound, computed tomography (CT), infrared or video,are used to communicate the visual information. Manipula-tors that are controlled by the surgeon throughout the wholeoperating procedure may use video, infrared or ultrasound incombination to give the surgeon visual cues as to the positionof the instruments. For example, the da Vinci SurgicalSystem, a master–slave remote manipulator, in which thesurgeon (master) remotely directs the robot (slave) througheach task, uses stereo endoscopes to give the surgeon a 3Dview of the region of surgery. The image acquisition aspect ofa surgical robot becomes particularly important if the robot isto perform surgical tasks on its own. In this instance, theimage modalities used must be of a very high resolution andaccuracy, so that they are correctly interpreted by the imageprocessing algorithms in the computer. For soft tissue surger-ies, MRI is the imaging modality of choice, offering high-definition images that can easily be converted into 3Dvolumes to allow precise motion planning, trajectoryfollowing and target location. Alternatively, fluoroscopicmarkers can be inserted into a soft tissue to give the properorientation cues, but that is more invasive to the patient, andthus mainly used during testing procedures.

The third main component of the surgical robot, the compu-ter, performs two main roles. Its primary role is as a coordina-tor, which translates the human operator’s commands intospecific actions performed by the robot manipulator. In doingso, the computer employs powerful algorithms that use theimaging data as a reference in order to guide the manipulator toan anatomical target specified by the surgeon. Thus, thecomputer is the link between the ‘data world’ of medical infor-mation (images, sensors and databases) and the physical worldof surgical actions [3]. The computer’s secondary role is as a datarecorder, recording the data relevant to the surgery, such asmanipulator tracking and organ displacements. This data canthen be used to update the intraoperative sequences of thesurgery, via surgeon-assisted decision making.

Robotic systems involved in urological surgical procedurescan be grouped in two main categories according to their modeof operation [3]. The first category is comprised of computer-integrated surgical systems for which the operator defines thetask and the system accomplishes the task on its own. Suchsystems are image driven and are made to excel at reaching atarget specified by the surgeon. In the future, such systems areenvisioned to have the ability to perform integrative pre-operative planning and be capable of intraoperative decisionmaking, based on the changing intent of the surgeon, all whileminimizing the trajectory and target reaching errors.

The second category of urological robotic systems consists ofoperator-driven manipulators, which exhibit low integrationwith the medical environment, and where the surgeon continu-ously controls the position of the robot and decides what taskneeds to be performed. These systems are designed primarily toscale a surgeon’s movement, eliminate tremor and improveinstrument accuracy. Endoscopic manipulators such as theAutomatic Endoscopic System for Optimal Positioning(AESOP®) and the ZEUS™, a surgical robotic system,master–slave remote manipulator, both built by ComputerMotion (CA, USA), as well as the da Vinci master–slavemanipulator, built by Intuitive Surgical (CA, USA), fall underthis category.

History & past achievementsAs in other medical robotic fields, robots for prostaticsurgery evolved quite naturally from industrial robots.Robotic development in this field was slower than in ortho-pedics or neurosurgery owing to the challenges imposed bythe deformability and high mobility of urological organs [4].Investigators in this field saw the potential of fine-tuningand adapting different versatile multiple degree of freedomindustrial robots to perform specific surgical tasks. Ofcourse, a couple of critical modifications were necessary,considering the working conditions of the industrial robotand the transplanted habitat in which the surgical robot

would be performing.Most importantly, safety issues regard-

ing the movement, working tolerancesand positioning of the robot had to beconsidered. Most industrial robots workin environments that are off-limits tohumans and so large motion envelopesand rapid position changes are notdangerous to personnel. Moreover, theworking tolerances of industrial robots,while precise, are not as precise as oper-ating on human tissue would require.Thus, once in the operating room, spaceand human proximity become crucialissues. Important considerations arise,such as streamlining a robot’s silhouetteand motion envelope as much as possi-ble, owing to space constraints. Another

Figure 1. The remote center of motion (RCM) concept as it is typically used in surgical robots.

RCM

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equally important factor is the robot’s synergy with othermedical equipment such as MRI scanners whoseperformance is affected by the presence of electronics.

The robot’s movements had to be limited and slowed downconsiderably so that they would not pose a threat to the patientand nearby doctors. This was usually achieved by regearing themechanical drives with larger gears and more precise actuatorsfor slower movement. Often, the robot’s control electronicswould also be changed to achieve slower, overdamped move-ment to ensure a precise motion envelope. The latter wouldalso ensure a better working tolerance.

The positioning of surgical robots also took on newchallenges from their industrial predecessors. Most crucially,the positioning of the robot had to be very precise to avoid anycomplications during surgery. It was very important that oncepositioned into a task, the robot would remain in that positionuntil the end of the task, even during a power outage. Thesafest and most efficient method devised was to move the robotinto the required position before the operation and then poweroff the components of the robot that were no longer neededduring the surgery.

In addition, designers of surgical robots sought to takeadvantage of other powerful techniques already in use in themedical field such as MRI scanners. Since these devices areeasily affected by, and can disrupt, electronic communication,special design characteristics had to be adopted to assurecoexistence in the operating room. Researchers turned to moreexpensive paramagnetic materials to construct the robot’s bodywith fiber optic sensors and wiring in order to eliminateelectronic interference.

The first pioneers to successfully answer the challenge ofconstructing and using a surgical robot in the operating roomwere Imperial College (London, UK), based Davies ‘Mecha-tronics in Medicine’ group [6]. In 1988, Davies sought to use anindustrial Puma 560® (RimLab) six degrees of freedom (DOF)industrial robot to perform a transurethral resection of theprostate (TURP) [5]. The original robotic concept provedinadequate for the conical prostate resection geometry requiredand two additional frames contributing two DOF were added tothe robot, for a total eight DOF system. Since the Puma 560part of the system was only used to position the robot in place,while the additional frames contributed to the cutting, it wasdecided that the Puma 560 should be replaced with a manipula-tor that focused specifically on positioning the prostate-resectingframework. Therefore, by limiting its motion envelope and itsDOF, the robot was kept simple, slender and safe, and wastailored to perform a specific task. Indeed, after a specialpurpose manual framework on performing the prostateresection was designed in 1989, a robotic motorized system‘Surgeon Assistant Robot for Prostatectomy’ (SARP) wassuccessfully built and clinically tested in April 1991, making itthe first active robot used to remove patient tissue [6].

A second-generation prostate resection robot, the ‘Probot’,presented in 1995 by Davies and largely based on the systempresented in 1991, has been introduced and used in clinical

trials at Guy’s Hospital (London, UK) [7]. The Probot is basedon the concept of a passive rigid mounting frame being used toposition and support the smaller motorized robot, whichresects the prostate. An easy to use intuitive program allows thesurgeon to measure the prostate and select the resection geo-metry on the touch screen. Tests with the robot have shown itsability to consistently perform the surgeon-specified resectionswithin acceptable error boundaries [8].

The initial success of the Probot has continued with furtherdevelopments of the prototype by the Sing Computer-Integrated Medical Intervention (CIMI) Research Group atNanyang Technological University, Singapore. Sing, one of thefounding research members of SARP, has taken the originalconcept and produced a universal platform named URobot,which is designed to be used with different treatment modali-ties, such as interstitial laser coagulation, laser resection andTURP, to treat prostate enlargement [9]. This prototypeplatform, named Surgeon Programmable Urological Device(SPUD) in medical literature, is meant to be both a therapeuticand a learning tool for urological surgeons. In 1998, SPUDentered clinical trials in Changi General Hospital (Singapore).

Noteworthy in the domain of robotic brachytherapy ofprostate cancer, is the Chinzei group from the National Insti-tute of Advanced Industrial Science and Technology (AIST),(Tokyo, Japan). In 2000, the group ran preclinical studies atBrigham and Women’s Hospital in (MA, USA), for a robotconceived to assist the surgeon with needle insertion into thebody. The robot’s rigid arms can hold, rotate and insert theneedle according to a radiologist’s predefined trajectory. Inter-estingly, the Brigham MRI robot is the first robot intended tobe MRI compatible. The system was designed to coexist withpowerful MRI systems; this posed new challenges in terms ofcontroller and body design. Electric fields picked up by MRIscanners lead to poorer quality images, and the pulsatingmagnetic fields emitted by the scanners not only attractmetallic objects, but also disrupt and destroy electrical systems.Therefore, a new approach to the robot’s sensors and compo-nents was devised. The body of the Brigham MRI robot iscompletely constructed of paramagnetic materials. None of itssensors (such as the ultrasound distance range finders) aremagnetic and robot communication in the proximity of theMRI scanner is achieved via fiber optics to avoid noise inter-ference. The preclinical tests performed on this system demon-strated that the robot can coexist with both surgeon and MRIscanner, without disrupting the work of either [10]. Specifically,the Chinzei group work has shown that coexistence of medicalrobots with restrictive image modalities, such as MRI, is notonly possible but truly beneficial.

The achievements of Rovetta and colleagues from the Poly-technic Institute (Milan, Italy), in the field of image-guidedrobotic prostate surgery are equally important. In 1995, thegroup was able to demonstrate a long desired goal of medicalrobotics, namely the use of image processing for achievingautomatic guidance of the robot [11]. The robot performed atransperineal prostate biopsy with the use of transrectal

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ultrasound (TRUS) and external video cameras. The TRUSwas used to image the prostate while the external video camerasrecorded the patient’s anatomy, position and movement. Fromthe two image modalities, image processing data was used tocreate a dynamic 3D model of the prostate; this allowed forneedle placement in the 3D space of the prostate with anaccuracy of 1–2 mm. This accuracy did not depend on thesurgeon’s chosen biopsy site for the robot [12].

Perhaps the best known achievements in the field of medicalrobotics, and prostate surgical robotics in particular, are theZEUS and the da Vinci master–slave telemanipulator systems.These systems made their appearance in 1997 and 1998,respectively, and are only a few of a handful of medical roboticassistants to have received US FDA approval; others include theAESOP and HERMES™, which are both built by ComputerMotion [13]. Both systems are remarkably similar in that theyconsist of robotic arms positioned next to the patient and asurgeon’s console, whose location is independent of the roboticarms, thereby allowing for the possibility of performing thesurgery remotely. One of the arms performs the task of holdingthe camera, while the other arms hold various instruments thatthe surgeon can manipulate from the remote console. Initially,the da Vinci’s instruments had seven DOF, making it advanta-geous over the ZEUS, which had five in the early versions, andlater versions had six DOF with the addition of tips that couldarticulate in a single plane (MicroWrist®, Computer Motion).However, the ZEUS system had telementoring capabilities,allowing the hook-up of another system (Socrates™, Compu-ter Motion) which could allow a surgeon in another location toinstruct the console operator during the surgical procedure. In2003, the makers of the ZEUS and da Vinci merged and theda Vinci system is currently the most widespread medical robotallowed for hospital use. The ZEUS system is no longer offeredfor sale, however, support continues to be provided for therobots that are still in use.

Present robotic applications in prostate surgeryIn this section we will focus on robotic camera holding systemsand the da Vinci Surgical System, which is the only roboticsystem currently available for assistance in prostate surgery.

Robotic camera holding systems In 1993, AESOP became the first surgical robotic system to beapproved by the US FDA and it remains a widely used system.The AESOP is a table-mounted robotic arm with six DOF, twoof which are passive and it is a particular implementation of theRCM concept. AESOP is composed of a planar two DOFmanipulator attached to a vertical translation stage. The trans-lation stage is attached to the operating table and the robotend-effector accommodates the laparoscope through a passivetwo DOF joint. A final rotation allows for orientation. Whenthe endoscope is passed through the entry port, its motion isrestricted to three rotations about the entry point and onetranslation about the endoscope axis [4]. As a result, the AESOPcan not only precisely manipulate a standard laparoscope or

other instrument but it is also designed to eliminate thecamera-holding assistant. It is controlled by the primarysurgeon either by hand, foot or via a voice control interface andit provides a stable view of the operating field. In an earlyclinical study, AESOP was found to decrease unwanted cameramovements and to provide a better image without increasingoperative time [14]. The use of one or more AESOP systems hasbeen shown to allow a surgeon to perform solo laparoscopicoperations without a camera holder or surgical assistant [15].Various laparoscopic operations have been successfullyperformed with the assistance of the AESOP, including radicalprostatectomy [16].

EndoAssist™ (Armstrong Healthcare) is another roboticcamera holding system that has recently been introduced intoclinical practice. This device is a freestanding laparoscopiccamera manipulator controlled by infrared signals from a head-set worn by the operator. The head movements to controlEndoAssist can be rapidly learned by the surgeon, and the setupand dismantling times are less than 10 min [17]. Overall, thissystem has proven to be practical and safe, and reduces operat-ing times compared with a skilled human camera-holdingassistant [18]. In another study, the EndoAssist robot was sig-nificantly quicker compared with the AESOP device; this wasattributed to the increased accuracy of movement in theEndoAssist compared with the voice recognition errorsoccurring while operating with the AESOP [19].

da Vinci Surgical SystemThe da Vinci Surgical System represents an improved andrenamed version of the MONA™, prototype surgical assist-ance equipment [20], that served as the first prototype surgicalsystem developed at the Stanford Research Institute, (CA,USA) [21]. Its master–slave concept involves a master unit thatthe surgeon controls. The surgeon’s commands (movements)are processed by a computer and sent to the ‘slave’ componentsthat carry out the task at hand in real time. Master–slave typesof systems were first introduced in the 1990s [22,23]. Usingmaster–slave robots, a surgeon seated at a console manipulateslevers that control mechanical instruments inside a patient’sbody. These systems represent a paradigm shift in surgerybecause the physician is no longer manipulating surgical instru-ments directly. Hence, these systems have great potential forremote telesurgery.

Apart from the master unit, the da Vinci system consists of athree- or four-arm surgical manipulator. The surgeon sits atthe control unit and is presented with a high-resolution,6–10 times magnified 3D view of the surgical field, which isachieved via two separate lenses positioned on the robotictower for binocular view. The console is ergonomicallydesigned and the surgeon’s hand–eye axis is positioned tocreate the illusion of operating directly on the patient. Thearms of the surgical manipulator are used to control thelaparoscope and for manipulating surgical instruments. Eachmotion of the operator’s hands is translated to a movement ofthe surgical instruments implementing the RCM principle.

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Information processing eliminates the fulcrum effect inherentto conventional laparoscopic surgery and thereby makes intra-corporeal manipulation more intuitive. Additionally, theinformation processing allows the robotic system to filter outphysiological tremors and to increase movement precision bymotion scaling. Motion scaling is the concept that a move-ment by the operator at the master unit can be amplified ordampened at the end-effector slave unit [4]. Depending on theend-effector in use, the instrumentation provides seven DOF,including rotations aimed at reproducing the human wrist.The 3D view of the surgical field helps the surgeon toaccomplish tasks such as intracorporeal suturing, which arevery challenging to master in conventional laparoscopy.

The da Vinci system was first used in Europe for cardiacsurgery and received FDA approval in July 2000. Since then,the system has been used in a variety of urological applica-tions but it has gained most attention in robot-assistedlaparoscopic radical prostatectomy (LRP) [24–27]. Schuesslerand colleagues reported the initial case of conventional LRPin 1997 [28]. Guillonneau and Vallancien [29], and Abbou andcolleagues [30] refined and popularized this minimallyinvasive approach. Conventional LRP, however, has provento be a challenging operation requiring advanced laparo-scopic skills. The lack of a 3D visual field and the limiteddexterity of conventional laparoscopy limit the surgeon’sworking space and complicate tasks such as suturing andintracorporeal knot tying. To facilitate this procedure, severalgroups have developed robot-assisted LRP programs [31–34].Meanwhile, significant experience with robot-assisted LRPhas accumulated [35], and excellent functional and early onco-logical results have been reported [36] that compare favorablywith the results of conventional LRP and open radical pros-tatectomy [37]. The learning curve for this very complexlaparoscopic procedure has been shown to be shorter usingthe robot-assisted approach compared with the conventionallaparoscopic technique [38–40]. Furthermore, Ahlering andcolleagues have shown that a laparoscopically naive yetexperienced open surgeon can successfully transfer their opensurgical skills to a laparoscopic environment with the help ofthe da Vinci robot [31]. Although suturing for the inexperi-enced is easier with the robot, laparoscopic knowledge is stillrequired, and the use of the robot also requires a significantlearning curve [41]. Correct trocar placement is necessary toprevent mechanical interference between the robotic arms;however, owing to the lack of tactile feedback, the surgeonmust develop an intuition about the suture tension in orderto avoid suture breakage and tissue strangulation. Theaspects of surgery that require gross, rather than precise,movements, such as the reflection of the bowel or countertraction during dissection, are more difficult with the roboticarms and so laparoscopic surgeons experienced with intra-corporeal suturing may not find the robot helpful [42]. Inaddition, problems associated with cost, maintenance, func-tional storage and use must be taken into consideration withthis complex and expensive technology. For example, in 2006

a three-arm da Vinci system cost US$1.12 million and afour-arm da Vinci cost US$1.3 million. Annual contract feesrange between US$120,000–140,000. Moreover, theda Vinci system’s instruments are limited to a life cycle of tenuses and the replacement costs per instrument are betweenUS$1200–4600. Finally, the system at the current configura-tion is bulky and requires large operating rooms. For thisreason, presurgery set-up times add considerably to the totalduration of the procedure.

Future robotic applications in prostate interventionsRobotic surgical technology may still be in its infancy, but overa short period its history is remarkable for large advances in thetechnological aspects of the field of urology. To get an idea ofthe potential growth of this field, it is enough to compare thenumber of robot-assisted radical prostatectomy (RP) pro-cedures in the last 5 years; 247 procedures were performed in2001, followed by 766, 2648, 8642 and 16,000 in 2002, 2003,2004 and 2005, respectively. By 2006, it is estimated that a full25,000 or a quarter of the 100,000 RP procedures performedin the USA will be robot assisted [43].

It is highly likely that medical technology will continue toevolve very rapidly and that robotics will play an important rolein that progress inside and outside the field of urology. Forprostate interventions the near future will mostly bringimprovements on the currently existing robotic systems firstand foremost the da Vinci system. Future robots are desired tobe less expensive, smaller and capable of even smoother andmore precise motion. Another development that is eagerlyawaited is the addition of tactile and force feedback tomaster–slave systems. The absence of this so-called haptic feed-back is one of the most often quoted drawbacks of the da Vincisystem. Haptics is an active area of research within the engi-neering community [44,45] and much research has already beencarried out to investigate new kinds of tactile sensors [46–48].

Telesurgery is an additional application for current roboticsystems that may become generally available with improvedtechnical equipment. Telesurgery refers to active control ofthe surgical instruments by a surgeon located at a remotedistance from the operative theater with data transmitted overa telecommunications line [13]. Although telesurgery is alreadyfeasible today and a small number of isolated, yet spectacular,transatlantic telerobotic surgeries have been performed [49,50],technical obstacles, among other reasons, have been a primarylimitation to its widespread adoption. Telesurgical inter-ventions present many practical challenges and for this reasonthe FDA mandates the operating surgeon’s presence in thesame operating room as the patient. Signal latency resultingfrom long-distance transmission can cause a delay betweenthe time the surgeon moves an instrument and the time thatmovement is seen on the video image of the surgical field.Ideally, this signal delay should be less than 10 ms to preventovershooting of movements. Surgeons can compensate fordelays of up to 300 ms but longer delays will significantlyhinder remote task performance. For transport of the high

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number of audio, video and medical images required duringtelesurgery, dedicated asynchronous transfer mode lines areconsidered to be the most reliable and safe. Communicationdelays are dependent on the distance between the sites, butprevious experience (delays of up to 155 ms) and speed calcu-lations have shown that these delays are acceptable whenperforming earth-to-earth connections [51–53]. New high-speed, broadband technologies, such as cable modems anddigital subscriber lines are widely available and data trans-mission bandwidth with wireless technology has reachedlevels that can be used in telemedical applications. However,the availability of these technologies is not yet universal.Moreover, redundancy needs to be built into the system as aback-up against primary signal disruption [17]. The connec-tions used for the transfer of patient data should be secure,preventing interruption, redirection or tampering with sensi-tive information. Advanced encryption protocols are begin-ning to be applied with success. Telesurgery holds the promiseto provide specialized care in remote and underserved areas,including situations such as military operations and spacetravel. Telesurgery may also serve as an avenue to propagatenovel surgical techniques with expert surgeons guiding lessexperienced ones stepwise through infrequently performed ortechnically demanding operations. Finally, telemedicine inter-actions can increase patient access to physicians. Surgeonswith particular areas of expertise may operate at any hospitalaround the world, obviating time-consuming and logisticaltravel concerns for both patient and physician [17].

With very rapidly developing technology, however, the futurewill not just hold improvements on currently existing roboticsystems or new applications for them. There is great potentialfor the use of robots in medicine in general, as well as in pros-tate interventions in particular. To reach their full potentialrobots need to become more integrated systems linked to avail-able imaging modalities [54]. Like most modern medical imagers(e.g., CT and MRI), robots are digital devices. As such, theycan easily be programmed to navigate in the 3D coordinatedsystem of the respective imager. Moreover, robots are capable ofworking more accurately than humans. Therefore, robots areideal devices to improve image-guided interventions (IGIs),because the success of IGI typically depends on the quality ofthe image used for the visualization of the target, as well as onthe ability to deploy the procedure needle/probe accurately tothe desired target. Owing to its easy transperineal and trans-rectal accessability, the prostate is a good target for IGI-likebiopsy or brachytherapy.

MRI provides the best visualization of the prostate and itssurrounding anatomy [55], which should make it the imagemodality of choice for prostate IGI. The principal limitation toits routine use in IGI in general is the complex and challengingenvironment [56] inherent to MRI technology and theconstrained ergonomics of closed-bore scanners. So far, only alimited number of centers have reported their experience withMRI-guided prostatic interventions [57–60]. Ideally, MRI-guidance would be combined with the precision of robotic

manipulation. However, limited accessibility of the patientwithin the MRI scanner and incompatibility of most compo-nents commonly used in robotics, particularly electromag-netic motors, make the development of a MRI-guided robot avery difficult engineering task [61]. Previous research in thisfield has commonly relied on piezoelectric motors [62–64].These are magnetic free but employ high-frequency currentscreating image distortion if operated closer than 0.5 m fromthe MRI isocenter [63].

Recently in the authors’ laboratory, the first fully MRI-compatible robot was developed [65]. The device is designed toperform automated MRI-guided prostate brachytherapy and itis currently undergoing preclinical testing (FIGURE 2). The robotis a six position control DOF system, allowing precise needleand seed placement in the prostate. It is built using ceramic,plastic and nonferrous parts, all of which have been tested toensure full MRI compatibility. Furthermore, it is small enoughto elegantly fit standard MRI bores with a patient inside(FIGURE 3). Communication with the computer is achieved viafiber-optic wires and custom-built light encoders, which trans-mit information to the robot’s actuators. These actuators arenovel air-powered stepper motors capable of producing precisemovement with step increments of 0.083 mm. As such, therobot has no metallic or electronic components present in theMRI room. The robot’s control console allows remote connec-tivity from other users, thereby making the robot telesurgerycompatible. To the best of the author’s knowledge, this robot isthe first fully MRI-compatible surgical robot designed to date.

So far, preclinical tests with the system have shown that it iscapable of automated and highly accurate MRI-guided brachy-therapy seed placement within a closed-bore scanner and that it

Figure 2. MRI compatible robotic system designed to perform fully automated MRI-guided brachytherapy of the prostate. MRI: Magnetic resonance imaging.

Connecting hoses (6 m)

Controller unit(stays outside imager’s room)

Robot(interacts with thepatient in the MRI)

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does not deteriorate the quality of MRI [66]. By utilizing onlineMRI guidance, it is conceivable that a device like our roboticsystem would improve the accuracy of seed placement inprostate brachytherapy and permit a more customized andtargeted distribution of the radioactive sources. Improvementsin the placement of the radioactive sources are likely to translateinto better cancer control, as well as reduced irradiation ofhealthy tissue [67,68].

Advances in MRI technology, such as MR spectroscopicimaging, dynamic contrast-enhanced MRI, and the avail-ability of higher field strength scanners, make MRI anincreasingly attractive imaging modality for targeting prostatecancer [69–71]. MRI-compatible devices, like the presentedrobotic system, can be designed to take biopsies, inject liquidagents and insert cryotherapy or radiofrequency probes. Inthis way, a robot could potentially improve the performanceof MRI-guided procedures and IGI in general and also playan important role in the validation and application of newlytargeted procedures emerging for diagnosis and therapy ofprostatic disease.

As technical development and miniaturization continue, inthe more distant future micro- and nanorobots can be fore-seen to enter the field of medicine. These robots will use bio-logical components such as proteins, ATP motors and DNAfor structural, actuation and information storage components,respectively. They may enter the body via oral ingestion orinjection, and be biocompatible so that when their procedureis finished, the body may simply digest or expel themnaturally. With this vision in mind it is conceivable thatfuture generations of physicians will be able to treat diseasesand maybe even improve on nature on a molecular basis [72].From fully integrated operation rooms capable of linkingmultiple compatible devices together, to surgeons practicing

their art on patients thousands of miles away, to biomolecularand nanorobots, the future holds great promise for theadvancement of medicine.

Expert commentary & five-year viewUrology has always been, and will continue to be, at the forefrontof integrating innovative new technologies with standard surgicalprocedures. Current evidence of this is the successful symbiosisbetween doctor and robot in the operating room. With the assist-ance of the da Vinci surgical robot, LRPs are successfullyperformed in more and more operating rooms across the USAand Europe. Moreover, operating rooms across the world arebecoming communication hardwired to allow surgeons tomentor and participate in remote surgical procedures.

In the next 5 years, we expect robot-assisted surgical pro-cedures to become evermore numerous. Given that the use ofthe da Vinci surgical platform is easier for surgeons to learnthan conventional laparoscopy, we expect robot-assisted radi-cal prostatectomy to supersede the conventional laparoscopicprocedure. We also expect other improvements to be broughtto the robot, and other commercial systems to become avail-able to make the surgical platform even easier to use. Theseinclude haptic feedback to give the surgeon a sense of whatforces and obstacles are being experienced by the roboticarms, as well as better image acquisition that can even tracedesired trajectories for the surgeon to follow and highlightregions of interest to the surgery in general. Providing force-feedback in a local system is not an engineering challenge, butperhaps competition needs to motivate future developments.Telesurgery and telementoring capabilities may also beexpected in the next generation of robotic systems.

Furthermore, we expect medical robotic technology toadvance more in the next 5 years, specifically with respect toimage-guided interventions. We expect to see many promis-ing experimental findings that will show algorithms androbots increasingly able to perform complicated procedureswith a high degree of autonomy and precision. Thesemachines will be aided by software capable of distinguishingone organ from another, and of optimizing trajectory follow-ing of, for example, needle placement or prostate tissueremoval, with little input from the surgeon. The robots willbe made to work seamlessly with the imaging modalities theywill be using, be they MRI, CT or ultrasound. The integra-tion of robotics and imaging gives robots capabilities that areunattainable to humans, because unlike humans they aredigital devices.

Given the worldwide level of regulatory proceduresrequired for the commercialization of medical devices, thenovel technologies developed today will not immediately havea broad proliferation into clinical use. However, these areexpected to make a direct difference in patient care becausebetter technology equates to better medicine. Whichever wayone looks at it, whether from the point of view of theresearcher, physician, or that of the patient, we can say withconfidence: the best is yet to come.

Figure 3. The robot fits into a standard closed bore magnetic resonance imaging scanner along with the patient.

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Key issues

• Urology has always been at the forefront of integrating novel technologies into surgical procedures.

• Robots allow the surgeon to manipulate tools with increased accuracy, thereby potentially improving the outcome of a surgical procedure.

• The da Vinci® robotic system has become successfully integrated in the surgical treatment of localized prostate cancer.

• Currently used robots do not exploit the full potential of medical robotic systems. Progress is expected through integrating medical imaging to surgery and in robotic image-guided interventions.

• The presence of different types of imaging modalities in the operating room, together with the robot, requires that the robot is fully compatible with the other existing equipment. This is an especially important issue where magnetic resonance imaging scanners are used.

ReferencesPapers of special note have been highlighted as:• of interest•• of considerable interest

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Affiliations

• Michael Muntener, MD

The Johns Hopkins Medicine, URobotics Laboratory, Department of Urology, Baltimore, MD, USA

• Daniel Ursu, MS


• Alexandru Patriciu, PhD


• Doru Petrisor, PhD


• Dan Stoianovici, PhD

The Johns Hopkins Medicine, URobotics Laboratory, Department of Urology, Mason F Lord West Tower, Room W115, 5200 Eastern Avenue, Baltimore, MD 21224, USATel.: +1 410 550 1980Fax: +1 410 550 [email protected]://urology.jhu.edu/urobotics

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