Original Research
JOURNAL OF ENDOUROLOGY Volume XX, Number XX, XXXXXX 2014 ª Mary Ann Liebert, Inc. Pp. ---–--DOI: 10.1089/end.2014.0401
The SimPORTAL Fluoro-Less C-Arm Trainer: An Innovative Device for Percutaneous Kidney Access Domenico Veneziano, MD, FEBU,1 Arthur Smith, MD,2 Troy Reihsen,1 Jason Speich,1 and Robert M. Sweet, MD, FACS1
Abstract
Introduction and Objectives: Achieving proper renal access is arguably the most challenging component of percutaneous nephrolithotomy. A core skill required during this procedure is the use of C-arm fluoroscopic imaging and parallax techniques for proper needle insertion into a predetermined calyceal papilla. The trainers available for these skills include virtual reality (VR) simulators and physical models requiring actual fluoroscopy and radiation exposure precautions. In this study we present the successful proof-of-concept of a lowcost physical fluoro-less C-arm trainer (CAT) for training percutaneous renal access. Materials and Methods: The SimPORTAL CAT includes a mini C-arm for simulating fluoroscopic imaging and a silicon flank simulation model for needle insertion. The C-arm has two mounted video cameras and is jointed to tilt and rainbow. The flank model contains an anatomically accurate cast of the upper urinary tract, including the ureter, calyces, and the renal pelvis, with an overlay of ribs to visually and tactically simulate the 10th–12th ribs. The simulated fluoroscopic imaging is viewed on a computer screen allowing for real-time visualization. Preliminary surveys were completed by participants (n = 14) at a training course that took place in Hemel Hampsted to obtain information on the acceptability of version 2.1 of the model. Results: We have successfully created a fluoro-less CAT that achieves the goals of training percutaneous access of the kidney. All participants (100%) considered the concept of avoiding radiation exposure during training as a highly valuable feature. About 92.8% of the enrolled participants considered the CAT of at least equal value to existing VR training models. Conclusions: The fluoroscopy-less CAT is an economically feasible and accurate model for training parallax. It effectively replicates the functions of a C-arm X-ray system for percutaneous access to the kidney without any radiation exposure to the learner. Further studies will examine construct validity for training and assessing percutaneous access skills. tures are associated with higher rates of complications using either supine or prone patient position.6 The current method of acquiring the surgical skill to gain access for PCNL is on patients vis-a`-vis the traditional apprenticeship model and repetitive practice.7 Some studies8,9 suggest that competence in performing PCNL is reached after 60 cases and excellence after 115. Even more than operating time, radiation parameters are a valuable tool in the assessment of operative competence. A significant reduction in radiation exposure is seen between the 1st and 15th procedures.9 Current training systems exist. The systems described use virtual reality (VR) or fluoro-assisted biologic and synthetic models.3,10,11 VR models have demonstrated some validity evidence,12 but are expensive (between 100,000 and 150,000 USD per unit, considering yearly maintenance) and are not easily portable, which have limited their widespread use for training. An
Introduction
P
ercutaneous access and removal was a breakthrough minimally invasive approach for treating large, complex renal stones.1 While CT is useful for planning, actual percutaneous kidney access is typically performed with the aid of a real-time dynamic imaging modality, such as ultrasound and/or fluoroscopy. A survey2 by the European Section of Uro-Technologies (ESUT) revealed that, in daily practice, 70% of all responding urologists perform percutaneous nephrolithotomy (PCNL), with an average of 16.8 procedures a month,3 confirming that PCNL is still a very common procedure. In the United States, in 2003,4 just 11% of urologists were personally obtaining their own access. This data confirms that obtaining renal access is the most challenging part of PCNL.5 Moreover, multiple-access punc1 2
Department of Urology, University of Minnesota, Minneapolis, Minnesota. The Smith Institute for Urology, Long Island, New York.
1
2
VENEZIANO ET AL.
FIG. 1. Degrees of movement for tilt and rainbow.
ex-vivo organ model described by Jutzi et al. depends upon access to porcine materials and does not actually allow any Xray-guided puncture.13 Other bench models can be accessed under fluoroscopic guidance,10 but require access to an actual C-arm. Thus, they can only be used in a C-arm-compatible environment and they expose the trainee and trainer to significant doses of radiation.8 In this article, we describe the creation and proof-of-concept of an affordable, portable, highfidelity small-footprint C-arm trainer (CAT). The CAT is built to simulate percutaneous fluoro-guided procedures without the need of actual X-rays or dedicated environment.
Bruyere et al.14 was modified and a reproduction of the real pelvis/calices/ureter complex was made using a 3D printer. This piece was fixed inside a mold and transparent silicon was poured onto it, to achieve the final silicon block. The spinal column and 10th through 12th ribs were placed on the outside of the block, providing both tactile and visible landmarks. For the purpose of this study, a 1-cm synthetic stone was placed in the posterior middle calix as a target. To inject fluid into the silicon pelvis, a foley catheter was placed in the ureteral space of the block and the balloon was inflated with 4 cc. Simulated contrast was produced using a mix of water and acrylic paint (Fig. 5).
Materials and Methods Equipment
Preliminary evaluation
The CAT was conceived, designed, and engineered by SimPORTAL (University of Minnesota) in 2013. Initially a computer-assisted design model was created. The first experimental unit, used for this study (model 2.1), was produced with a rapid prototyping 3D printer (Stratasys, Eden Prairie, MN). The device was scaled to fit on a standard desk and accommodates tilt (-30/ +30) and rainbow (- 15/+ 55) (Fig. 1). Two webcams were mounted on the two tips of the C facing each other (Fig. 2). The cameras were connected via USB to an Apple Macbook Pro for video processing. Each image was obtained, filtered, and fused using the Hollywood video-processing technique called ‘‘blue screen’’ or ‘‘chroma key.’’ The images sent by the two webcams were overlaid using the aforementioned transparency filter and processed by a real-time broadcasting software (Camtwist for OSX), to achieve the final on-screen result. The simulated X-ray image was sent to a 42¢¢ on-wall monitor, in front of the training station (Fig. 3). For the purposes of this study, we created a transparent silicon flank model, representing a right kidney in prone position (Fig. 4). The casting technique previously used by
The CAT was tested during a hands-on urological course held in Hemel Hempstead (London, United Kingdom) in
FIG. 2. The two cameras (in the circles) and the real-time on-screen image.
FLUORO-LESS C-ARM TRAINER FOR PERCUTANEOUS KIDNEY ACCESS
3
advanced in the ‘‘Z’’ plane as the c-arm is rainbowed back to perpendicular to the calix.15 Subjects then performed the bull’s eye technique on the CAT, using a 16-gauge needle. The trial was considered successful when the needle touched the stone in the middle posterior calix. The number of puncture attempts was measured and the subjects evaluated the model. A soft-tip guidewire was available to assess with even more certainty the successful puncture of the calix. A ‘‘Simbionix’’ PERC Mentor VR system12 was made available for all participants to train on and make comparisons with the CAT. To provide also a physical training benchmark, the ‘‘Limbs and Things’’ PCNL trainer was available during the session. After having performed a training session with at least two puncture attempts on each simulator available, all of them filled out an electronic Likert scale survey. The questionnaire evaluated the effectiveness of CAT to perform the bull’s eye technique, the anatomic representation of the kidney model, the usefulness of the provided tactile and visual landmarks, the accuracy of the simulated X-ray image, the value of fluoro-less C-arm training, and the quality of the CAT compared to previously tested physical and VR systems. Results
FIG. 3.
The C-arm trainer (CAT) during the test course.
2013. A total of 14 urologists tested the training device. All participants were in their first post-residency year and had poor previous experience with X-ray-guided percutaneous kidney punctures. None of them declared any previous training session specific to this topic. After informed consent, subjects took part in a didactic lesson held by an expert about percutaneous kidney puncture and urolithiasis treatment. The bull’s eye technique of caliceal targeting was explained as the alignment of the needle, its hub, and the calix using the rainbow movement of the C-arm. Subsequently, the needle is
Twenty-six punctures were made on a total of two kidney models. After the first 21 punctures the first silicon block was substituted with a new one, as previous puncture tracks became visibly obvious. Every participant could perform two puncture attempts on the model. Eighteen of the 26 punctures (69.2%) successfully hit the provided stone in the calix. The survey showed (Fig. 6) that 13 participants (92.8%) would use the CAT to train novices in PERC and would use the CAT to demonstrate the bull’s eye technique. Twelve urologists (85.7%) considered the kidney model as an accurate anatomic representation with only one participant (7.1%) who did not agree with this statement. Ten participants (71.4%) considered the depicted landmarks as useful. The other four were neutral about this statement. Twelve attendants (85.7%) considered the X-ray-simulated image as an accurate representation of a real fluoroscopic image and all of them (100%) felt that avoiding radiation was important for training. Compared to other physical models the CAT has been considered as ‘‘same’’ or ‘‘better’’ by all participants (100%). Compared to PERC Mentor, the CAT has been classified as ‘‘same’’ or ‘‘better’’ by 13 attendants (92.8%) (Fig. 7). The use of the simulated contrast (produced by Sim PORTAL, University of Minnesota) did not affect the transparency of the silicon model or the quality of the simulated X-ray image. Discussion
FIG. 4. The silicon block uncovered. Spinal column and 10th through 12th ribs overlay provide tactile and visible landmarks.
PCNL is currently the most complicated stone surgery technique to teach.16 Inability to gain proper access can lead to increased costs in the form of additional equipment and supplies, consultations, secondary procedures, and operative time. It can also increase the risks of morbidity for our patients in the form of multiple tracks, blood loss, hemothorax, pneumothorax, as well as colon, spleen, or liver puncture. According to previous studies,17 the placement of a nephrostomy produces a mean fluoroscopic exposure time of 7 minutes and a mean entrance skin dose of 110 mGy. These data tend to increase when related to a whole PCNL
4
VENEZIANO ET AL.
FIG. 5. Simulated contrast injection. The sequence of images shows the behavior of contrast inside the silicon block.
procedure and to different parameters, such as patient BMI, position and dimension of the stone, or need for multiple accesses.18 The learning curve for access is significant for both urologists and radiologists. PercMentor (SimBionix, Lod, Israel) represented the first simulation systems to
FIG. 6.
demonstrate validity evidence as an effective training tool for these skills. The physical models using animal parts and cadaver kidneys take a substantial time to set up, are not consistent between models (which is a quality that is important for assessment), expose the users to unnecessary radiation
Data collected about the CAT during the course.
FLUORO-LESS C-ARM TRAINER FOR PERCUTANEOUS KIDNEY ACCESS
FIG. 7. Comparison between the CAT and the existing PERC simulators. and biologics, and require a facility that can accommodate fluoroscopy. CAT demonstrated good face and content validity in our cohort for training percutaneous access to the kidney and compared favorably with a gold-standard training model: the PercMentor. The CAT is a reproducible, realistic, portable, low-cost option for training and assessment. The system took just a few minutes to set up and the substitution of the silicon block did not cause any loss of time during the training session. By the end of the training session every participant successfully targeted the stone at least one time, helping to confirm the effectiveness of the instruction and functionality of the novel double-camera image guidance. One participant did not feel that the kidney model was an accurate anatomic representation. In retrospect, the cast was placed in the mold at 55, which indeed is atypical. This is easily correctable for future models. All other participants did not consider this anatomical representation to be a problem. The importance of the depicted landmarks was underestimated (71.4% considered them useful) because no specific CT scan was shown to any attendant before the session. This is the reason why no exact correlation between landmarks and inner structures was possible and consequentially useful to accomplish the procedure. In the future, providing the attendants with the CT scan to correlate with the model should add to the training value. Given the nature of the model’s design, whereby we 3D-print collecting-system casts based on clinical datasets, we can easily and rapidly create patient-specific rehearsal opportunities. The absolute importance of training without radiation exposure was clear to all participants (100%). The possibility to have a proper tactile feedback with the CAT while introducing guidewires or touching the stone with the needle tip was appreciated by the participants, which considered the CAT to be ‘‘same’’ or ‘‘better’’ compared to VR (PERC Mentor) in 92.8% of cases. The value of the CAT was even clearer when its potential cost was compared with the actual price of VR systems. The cost of a VR training device for percutaneous renal access starts indeed from 100,000 USD, while the CAT has an estimated
5
price of 4,000 USD. Even considering the need for a new kidney model after 21 puncture attempts, participants considered the difference of the overall management cost relevant. PERC Mentor system has been used as a comparative benchmark regarding price and reliability, being already studied for different validities with positive results.10–12 During the course, different physical PERC trainers were available for the subjects to be used. In this limited cohort, the CAT was considered as ‘‘better’’ than any other physical PERC simulators available or previously used. Performing preliminary validity studies during the prototype phase of simulator development is an important step to demonstrate utility and provide useful feedback toward a commercialized product (Sweet et al., Annals of Surgery). This pilot study of CAT demonstrated good acceptability and face and content validity, and provided valuable feedback to SimPORTAL as to the ways to improve the model. Evidence of construct validity on larger cohorts and on a multicentric scale will support an argument to integrate it further into courses and training programs. This will allow the educator to concentrate on teaching judgment and strengthening the knowledge and interpretation of what is observed in the clinical setting. Evidence of predictive validity, considered as the demonstration that surgical performance scores measured on the simulator during training predict the trainee’s future skill level when transferred to the operating room, could moreover explain how the CAT affects surgeons’ performance in reallife cases.19 The use of the correlating CT scan in conjunction with the exercise will enhance the learning experience. At the same time its low cost may allow practicing surgeons and radiologists who perform percutaneous access procedures sporadically, to maintain proficiency between cases.11 The CAT is not yet available on the market and is still in a prototyping phase. The University of Minnesota is still processing its concept design for copyright. Conclusions
The preliminary testing of our novel, portable C-arm training system for percutaneous renal punctures demonstrates the need for reliable and low-cost alternatives to VR systems. Our novel double-camera system, coupled to the processing software, is able to obtain visual information enough to accomplish correctly the training tasks, without expensive additional 3D motion-tracking technologies. It effectively and reliably replicates the functions of a real X-ray system, without any radiation exposure for percutaneous access to the kidney. Further studies will examine construct validity for training and assessing percutaneous access skills. Acknowledgment
SimPORTAL thanks Boston Scientific for access to their course in Hemel Hampsted. Disclosure Statement
No competing financial interests exist. References
1. Lee WJ, Smith AD, Cubelli V, Vernace FM. Percutaneous nephrolithotomy: Analysis of 500 consecutive cases. Urol Radiol 1986;8:61–66.
6
2. Kauer PC, et al. Present practice and treatment strategies in endourological stone management. Results of a survey of the European Society of Uro-technology (ESUT). Eur Urol 2005;48:182–188. 3. Ahmed K, et al. Effectiveness of procedural simulation in urology: A systematic review. J Urol 2011;186:26–34. 4. De la Rosette J, et al. The Clinical Research Office of the Endourological Society Percutaneous Nephrolithotomy Global Study: Indications, complications, and outcomes in 5803 patients. J Endourol 2011;25:11–17. 5. De la Rosette J, et al. Training in percutaneous nephrolithotomy—A critical review. Eur Urol 2008;54: 994–1003. 6. Astroza G, et al. Effect of supine vs prone position on outcomes of percutaneous nephrolithotomy in staghorn calculi: Results from the Clinical Research Office of the Endourology Society Study. Urology 2013;82:1240e1245. 7. Shalhav AL, Dabagia MD, Wagner TT, Koch MO, Lingeman JE. Training postgraduate urologists in laparoscopic surgery: The current challenge. J Urol 2002;167:2135–2137. 8. Allen D, et al. Defining the learning curve for percutaneous nephrolithotomy. J Endourol 2005;19:279–282. 9. Tanriverdi O, et al. The learning curve in the training of percutaneous nephrolithotomy. Eur Urol 2007;52:206–212. 10. Stern J, et al. Percutaneous renal access simulators. J Endourol 2007;21:270–273. 11. Wignall GR, et al. Surgical simulation: A urological perspective. J Urol 2008;179:1690–1699. 12. Mishra S, et al. Validation of virtual reality simulation for percutaneous renal access training. J Endourol 2010;4: 635–640. 13. Jutzi S, et al. New ex vivo organ model for percutaneous renal surgery using a laparoendoscopic training box: The sandwich model. World J Urol 2014;32:783–789.
VENEZIANO ET AL.
14. Bruyere F, et al. Rapid prototyping model for percutaneous nephrolithotomy training. J Endourol 2008;22:91– 96. 15. Steinberg PL, et al. Fluoroscopy-guided percutaneous renal access. J Endourol 2009;23:1627–1631. 16. Michiel MS, Trojan L, Rassweiler JJ. Complications in percutaneous nephrolithotomy. Eur Urol 2007;51:899– 906. 17. Mahadevappa M. Fluoroscopy: Patient radiation exposure issues. RadioGraphics 2001;21:1033–1045. 18. Mancini G, et al. Factors affecting patient radiation exposure during percutaneous nephrolithotomy. J Urol 2010;184: 2373–2377. 19. McDougall EM. Validation of surgical simulators. J Endourol 2007;21:244–247.
Address correspondence to: Domenico Veneziano Department of Urology University of Minnesota 1117 Marquette Avenue Minneapolis, MN 55403 E-mail: [email protected]
Abbreviations Used CAT ¼ C-arm trainer CT ¼ computed tomography PCNL ¼ percutaneous nephrolithotomy VR ¼ virtual reality
JOURNAL OF ENDOUROLOGY Volume XX, Number XX, XXXXXX 2014 ª Mary Ann Liebert, Inc. Pp. ---–--DOI: 10.1089/end.2014.0401
The SimPORTAL Fluoro-Less C-Arm Trainer: An Innovative Device for Percutaneous Kidney Access Domenico Veneziano, MD, FEBU,1 Arthur Smith, MD,2 Troy Reihsen,1 Jason Speich,1 and Robert M. Sweet, MD, FACS1
Abstract
Introduction and Objectives: Achieving proper renal access is arguably the most challenging component of percutaneous nephrolithotomy. A core skill required during this procedure is the use of C-arm fluoroscopic imaging and parallax techniques for proper needle insertion into a predetermined calyceal papilla. The trainers available for these skills include virtual reality (VR) simulators and physical models requiring actual fluoroscopy and radiation exposure precautions. In this study we present the successful proof-of-concept of a lowcost physical fluoro-less C-arm trainer (CAT) for training percutaneous renal access. Materials and Methods: The SimPORTAL CAT includes a mini C-arm for simulating fluoroscopic imaging and a silicon flank simulation model for needle insertion. The C-arm has two mounted video cameras and is jointed to tilt and rainbow. The flank model contains an anatomically accurate cast of the upper urinary tract, including the ureter, calyces, and the renal pelvis, with an overlay of ribs to visually and tactically simulate the 10th–12th ribs. The simulated fluoroscopic imaging is viewed on a computer screen allowing for real-time visualization. Preliminary surveys were completed by participants (n = 14) at a training course that took place in Hemel Hampsted to obtain information on the acceptability of version 2.1 of the model. Results: We have successfully created a fluoro-less CAT that achieves the goals of training percutaneous access of the kidney. All participants (100%) considered the concept of avoiding radiation exposure during training as a highly valuable feature. About 92.8% of the enrolled participants considered the CAT of at least equal value to existing VR training models. Conclusions: The fluoroscopy-less CAT is an economically feasible and accurate model for training parallax. It effectively replicates the functions of a C-arm X-ray system for percutaneous access to the kidney without any radiation exposure to the learner. Further studies will examine construct validity for training and assessing percutaneous access skills. tures are associated with higher rates of complications using either supine or prone patient position.6 The current method of acquiring the surgical skill to gain access for PCNL is on patients vis-a`-vis the traditional apprenticeship model and repetitive practice.7 Some studies8,9 suggest that competence in performing PCNL is reached after 60 cases and excellence after 115. Even more than operating time, radiation parameters are a valuable tool in the assessment of operative competence. A significant reduction in radiation exposure is seen between the 1st and 15th procedures.9 Current training systems exist. The systems described use virtual reality (VR) or fluoro-assisted biologic and synthetic models.3,10,11 VR models have demonstrated some validity evidence,12 but are expensive (between 100,000 and 150,000 USD per unit, considering yearly maintenance) and are not easily portable, which have limited their widespread use for training. An
Introduction
P
ercutaneous access and removal was a breakthrough minimally invasive approach for treating large, complex renal stones.1 While CT is useful for planning, actual percutaneous kidney access is typically performed with the aid of a real-time dynamic imaging modality, such as ultrasound and/or fluoroscopy. A survey2 by the European Section of Uro-Technologies (ESUT) revealed that, in daily practice, 70% of all responding urologists perform percutaneous nephrolithotomy (PCNL), with an average of 16.8 procedures a month,3 confirming that PCNL is still a very common procedure. In the United States, in 2003,4 just 11% of urologists were personally obtaining their own access. This data confirms that obtaining renal access is the most challenging part of PCNL.5 Moreover, multiple-access punc1 2
Department of Urology, University of Minnesota, Minneapolis, Minnesota. The Smith Institute for Urology, Long Island, New York.
1
2
VENEZIANO ET AL.
FIG. 1. Degrees of movement for tilt and rainbow.
ex-vivo organ model described by Jutzi et al. depends upon access to porcine materials and does not actually allow any Xray-guided puncture.13 Other bench models can be accessed under fluoroscopic guidance,10 but require access to an actual C-arm. Thus, they can only be used in a C-arm-compatible environment and they expose the trainee and trainer to significant doses of radiation.8 In this article, we describe the creation and proof-of-concept of an affordable, portable, highfidelity small-footprint C-arm trainer (CAT). The CAT is built to simulate percutaneous fluoro-guided procedures without the need of actual X-rays or dedicated environment.
Bruyere et al.14 was modified and a reproduction of the real pelvis/calices/ureter complex was made using a 3D printer. This piece was fixed inside a mold and transparent silicon was poured onto it, to achieve the final silicon block. The spinal column and 10th through 12th ribs were placed on the outside of the block, providing both tactile and visible landmarks. For the purpose of this study, a 1-cm synthetic stone was placed in the posterior middle calix as a target. To inject fluid into the silicon pelvis, a foley catheter was placed in the ureteral space of the block and the balloon was inflated with 4 cc. Simulated contrast was produced using a mix of water and acrylic paint (Fig. 5).
Materials and Methods Equipment
Preliminary evaluation
The CAT was conceived, designed, and engineered by SimPORTAL (University of Minnesota) in 2013. Initially a computer-assisted design model was created. The first experimental unit, used for this study (model 2.1), was produced with a rapid prototyping 3D printer (Stratasys, Eden Prairie, MN). The device was scaled to fit on a standard desk and accommodates tilt (-30/ +30) and rainbow (- 15/+ 55) (Fig. 1). Two webcams were mounted on the two tips of the C facing each other (Fig. 2). The cameras were connected via USB to an Apple Macbook Pro for video processing. Each image was obtained, filtered, and fused using the Hollywood video-processing technique called ‘‘blue screen’’ or ‘‘chroma key.’’ The images sent by the two webcams were overlaid using the aforementioned transparency filter and processed by a real-time broadcasting software (Camtwist for OSX), to achieve the final on-screen result. The simulated X-ray image was sent to a 42¢¢ on-wall monitor, in front of the training station (Fig. 3). For the purposes of this study, we created a transparent silicon flank model, representing a right kidney in prone position (Fig. 4). The casting technique previously used by
The CAT was tested during a hands-on urological course held in Hemel Hempstead (London, United Kingdom) in
FIG. 2. The two cameras (in the circles) and the real-time on-screen image.
FLUORO-LESS C-ARM TRAINER FOR PERCUTANEOUS KIDNEY ACCESS
3
advanced in the ‘‘Z’’ plane as the c-arm is rainbowed back to perpendicular to the calix.15 Subjects then performed the bull’s eye technique on the CAT, using a 16-gauge needle. The trial was considered successful when the needle touched the stone in the middle posterior calix. The number of puncture attempts was measured and the subjects evaluated the model. A soft-tip guidewire was available to assess with even more certainty the successful puncture of the calix. A ‘‘Simbionix’’ PERC Mentor VR system12 was made available for all participants to train on and make comparisons with the CAT. To provide also a physical training benchmark, the ‘‘Limbs and Things’’ PCNL trainer was available during the session. After having performed a training session with at least two puncture attempts on each simulator available, all of them filled out an electronic Likert scale survey. The questionnaire evaluated the effectiveness of CAT to perform the bull’s eye technique, the anatomic representation of the kidney model, the usefulness of the provided tactile and visual landmarks, the accuracy of the simulated X-ray image, the value of fluoro-less C-arm training, and the quality of the CAT compared to previously tested physical and VR systems. Results
FIG. 3.
The C-arm trainer (CAT) during the test course.
2013. A total of 14 urologists tested the training device. All participants were in their first post-residency year and had poor previous experience with X-ray-guided percutaneous kidney punctures. None of them declared any previous training session specific to this topic. After informed consent, subjects took part in a didactic lesson held by an expert about percutaneous kidney puncture and urolithiasis treatment. The bull’s eye technique of caliceal targeting was explained as the alignment of the needle, its hub, and the calix using the rainbow movement of the C-arm. Subsequently, the needle is
Twenty-six punctures were made on a total of two kidney models. After the first 21 punctures the first silicon block was substituted with a new one, as previous puncture tracks became visibly obvious. Every participant could perform two puncture attempts on the model. Eighteen of the 26 punctures (69.2%) successfully hit the provided stone in the calix. The survey showed (Fig. 6) that 13 participants (92.8%) would use the CAT to train novices in PERC and would use the CAT to demonstrate the bull’s eye technique. Twelve urologists (85.7%) considered the kidney model as an accurate anatomic representation with only one participant (7.1%) who did not agree with this statement. Ten participants (71.4%) considered the depicted landmarks as useful. The other four were neutral about this statement. Twelve attendants (85.7%) considered the X-ray-simulated image as an accurate representation of a real fluoroscopic image and all of them (100%) felt that avoiding radiation was important for training. Compared to other physical models the CAT has been considered as ‘‘same’’ or ‘‘better’’ by all participants (100%). Compared to PERC Mentor, the CAT has been classified as ‘‘same’’ or ‘‘better’’ by 13 attendants (92.8%) (Fig. 7). The use of the simulated contrast (produced by Sim PORTAL, University of Minnesota) did not affect the transparency of the silicon model or the quality of the simulated X-ray image. Discussion
FIG. 4. The silicon block uncovered. Spinal column and 10th through 12th ribs overlay provide tactile and visible landmarks.
PCNL is currently the most complicated stone surgery technique to teach.16 Inability to gain proper access can lead to increased costs in the form of additional equipment and supplies, consultations, secondary procedures, and operative time. It can also increase the risks of morbidity for our patients in the form of multiple tracks, blood loss, hemothorax, pneumothorax, as well as colon, spleen, or liver puncture. According to previous studies,17 the placement of a nephrostomy produces a mean fluoroscopic exposure time of 7 minutes and a mean entrance skin dose of 110 mGy. These data tend to increase when related to a whole PCNL
4
VENEZIANO ET AL.
FIG. 5. Simulated contrast injection. The sequence of images shows the behavior of contrast inside the silicon block.
procedure and to different parameters, such as patient BMI, position and dimension of the stone, or need for multiple accesses.18 The learning curve for access is significant for both urologists and radiologists. PercMentor (SimBionix, Lod, Israel) represented the first simulation systems to
FIG. 6.
demonstrate validity evidence as an effective training tool for these skills. The physical models using animal parts and cadaver kidneys take a substantial time to set up, are not consistent between models (which is a quality that is important for assessment), expose the users to unnecessary radiation
Data collected about the CAT during the course.
FLUORO-LESS C-ARM TRAINER FOR PERCUTANEOUS KIDNEY ACCESS
FIG. 7. Comparison between the CAT and the existing PERC simulators. and biologics, and require a facility that can accommodate fluoroscopy. CAT demonstrated good face and content validity in our cohort for training percutaneous access to the kidney and compared favorably with a gold-standard training model: the PercMentor. The CAT is a reproducible, realistic, portable, low-cost option for training and assessment. The system took just a few minutes to set up and the substitution of the silicon block did not cause any loss of time during the training session. By the end of the training session every participant successfully targeted the stone at least one time, helping to confirm the effectiveness of the instruction and functionality of the novel double-camera image guidance. One participant did not feel that the kidney model was an accurate anatomic representation. In retrospect, the cast was placed in the mold at 55, which indeed is atypical. This is easily correctable for future models. All other participants did not consider this anatomical representation to be a problem. The importance of the depicted landmarks was underestimated (71.4% considered them useful) because no specific CT scan was shown to any attendant before the session. This is the reason why no exact correlation between landmarks and inner structures was possible and consequentially useful to accomplish the procedure. In the future, providing the attendants with the CT scan to correlate with the model should add to the training value. Given the nature of the model’s design, whereby we 3D-print collecting-system casts based on clinical datasets, we can easily and rapidly create patient-specific rehearsal opportunities. The absolute importance of training without radiation exposure was clear to all participants (100%). The possibility to have a proper tactile feedback with the CAT while introducing guidewires or touching the stone with the needle tip was appreciated by the participants, which considered the CAT to be ‘‘same’’ or ‘‘better’’ compared to VR (PERC Mentor) in 92.8% of cases. The value of the CAT was even clearer when its potential cost was compared with the actual price of VR systems. The cost of a VR training device for percutaneous renal access starts indeed from 100,000 USD, while the CAT has an estimated
5
price of 4,000 USD. Even considering the need for a new kidney model after 21 puncture attempts, participants considered the difference of the overall management cost relevant. PERC Mentor system has been used as a comparative benchmark regarding price and reliability, being already studied for different validities with positive results.10–12 During the course, different physical PERC trainers were available for the subjects to be used. In this limited cohort, the CAT was considered as ‘‘better’’ than any other physical PERC simulators available or previously used. Performing preliminary validity studies during the prototype phase of simulator development is an important step to demonstrate utility and provide useful feedback toward a commercialized product (Sweet et al., Annals of Surgery). This pilot study of CAT demonstrated good acceptability and face and content validity, and provided valuable feedback to SimPORTAL as to the ways to improve the model. Evidence of construct validity on larger cohorts and on a multicentric scale will support an argument to integrate it further into courses and training programs. This will allow the educator to concentrate on teaching judgment and strengthening the knowledge and interpretation of what is observed in the clinical setting. Evidence of predictive validity, considered as the demonstration that surgical performance scores measured on the simulator during training predict the trainee’s future skill level when transferred to the operating room, could moreover explain how the CAT affects surgeons’ performance in reallife cases.19 The use of the correlating CT scan in conjunction with the exercise will enhance the learning experience. At the same time its low cost may allow practicing surgeons and radiologists who perform percutaneous access procedures sporadically, to maintain proficiency between cases.11 The CAT is not yet available on the market and is still in a prototyping phase. The University of Minnesota is still processing its concept design for copyright. Conclusions
The preliminary testing of our novel, portable C-arm training system for percutaneous renal punctures demonstrates the need for reliable and low-cost alternatives to VR systems. Our novel double-camera system, coupled to the processing software, is able to obtain visual information enough to accomplish correctly the training tasks, without expensive additional 3D motion-tracking technologies. It effectively and reliably replicates the functions of a real X-ray system, without any radiation exposure for percutaneous access to the kidney. Further studies will examine construct validity for training and assessing percutaneous access skills. Acknowledgment
SimPORTAL thanks Boston Scientific for access to their course in Hemel Hampsted. Disclosure Statement
No competing financial interests exist. References
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Address correspondence to: Domenico Veneziano Department of Urology University of Minnesota 1117 Marquette Avenue Minneapolis, MN 55403 E-mail: [email protected]
Abbreviations Used CAT ¼ C-arm trainer CT ¼ computed tomography PCNL ¼ percutaneous nephrolithotomy VR ¼ virtual reality
