[Simulation-based training in urology: A systematic literature review]. / Formation par la simulation : de quels outils disposons-nous en urologie ? Revue systématique de la littérature.

CONTEXT: Simulation-based training is taking an increasingly important place in surgical training and is becoming mandatory with the latest reform of the French medical studies. OBJECTIVES: The objectives of this work were to report the various simulation tools available for the surgical training in urology, along with their validation level, through a systematic literature review. DOCUMENTARY SOURCES: A search was conducted using Medline® with the terms "urology" and "simulator". Articles in English and French were selected. STUDY SELECTION: Two hundred and ninety-one abstracts were read, allowing for the selection of 154 articles read to assess their eligibility. Studies whose main objective was not the validation of a simulator, studies describing animal models or studies whose full text was not available were excluded. RESULTS: One hundred and six studies were analyzed in this review. The simulators described were classified in 7 categories: laparoscopic surgery, robotic surgery, ureteroscopy, percutaneous nephrolithotomy, endoscopic bladder and prostate surgery, basic skills in urology, and ultrasound-guided prostate interventions simulators. Apparent and content validity were demonstrated for most simulators, but construct and predictive validity were often lacking. LIMITATIONS: We did not consider the use of simulators as competency evaluation tools. Besides, the latest terminology proposed to define the various validation steps was not taken into account. CONCLUSION: Many simulators are available in the field of urology and allow the reproduction of a large variety of urological procedures. However, their validation level is inconsistent, and has to be taken into account when choosing a simulator for surgical training, along with its cost, the eagerness of students to use the simulator and its availability.

[MRI-guided targeted prostate biopsies in the diagnosis of prostate cancer: a systematic literature review]. / Biopsies prostatiques ciblées guidées par IRM dans le diagnostic du cancer de prostate : revue de la littérature.

INTRODUCTION: Advances in MRI technology for detection of prostate cancer allow targeted biopsies of suspicious areas. MATERIAL AND METHODS: A systematic literature review was performed on Medline(®) with the keywords "targeted", "prostate biopsy" and related articles. We studied 65 abstracts and 102 related abstracts, read 38 articles and selected 27 articles. RESULTS: Mental reconstruction gives way for targeted biopsies by direct MRI guidance inside the MRI, and MRI-TRUS fusion. The first option offers high precision targeting but is limited by the accessibility, cost and duration of the procedure. MRI-TRUS image fusion is a promising compromise. Cancer detection rates vary from 15 to 64 %. CONCLUSION: Biopsies targeting suspicious areas on MRI are promising to improve the sensitivity and performance of prostate biopsies.

Fluoroscopy-based navigation system in spine surgery.

The variability in width, height, and spatial orientation of a spinal pedicle makes pedicle screw insertion a delicate operation. The aim of the current paper is to describe a computer-assisted surgical navigation system based on fluoroscopic X-ray image calibration and three-dimensional optical localizers in order to reduce radiation exposure while increasing accuracy and reliability of the surgical procedure for pedicle screw insertion. Instrumentation using transpedicular screw fixation was performed: in a first group, a conventional surgical procedure was carried out with 26 patients (138 screws); in a second group, a navigated surgical procedure (virtual fluoroscopy) was performed with 26 patients (140 screws). Evaluation of screw placement in every case was done by using plain X-rays and post-operative computer tomography scan. A 5 per cent cortex penetration (7 of 140 pedicle screws) occurred for the computer-assisted group. A 13 per cent penetration (18 of 138 pedicle screws) occurred for the non computer-assisted group. The radiation running time for each vertebra level (two screws) reached 3.5 s on average in the computer-assisted group and 11.5 s on average in the non computer-assisted group. The operative time for two screws on the same vertebra level reaches 10 min on average in the non computer-assisted group and 11.9 min on average in the computer-assisted group. The fluoroscopy-based (two-dimensional) navigation system for pedicle screw insertion is a safe and reliable procedure for surgery in the lower thoracic and lumbar spine.

[Accuracy measurements of acetabular cup positioning using CT less navigation]. / Protocole d'évaluation du risque d'erreur dans le positionnement cotyloïdien par navigation sans imagerie tomodensitométrique préopératoire.

PURPOSE OF THE STUDY: Standard methodology is lacking for evaluating the accuracy of surgical navigation systems. The purpose of the present study was to propose a new approach to error measurements of an image-free navigation system used for total hip arthroplasty. MATERIAL AND METHODS: This new approach evaluates the overall accuracy of the system and quantifies the influence of clinical application on this global error. The majority of hip navigation systems use the anterior pelvic plane as part of the reference system. With image-free systems, anatomic pelvic landmarks must be acquired intraoperatively in order to define the anterior pelvic plane. This step could potentially introduce a significant error for navigation. Two studies were performed to measure this error, one on patients and the other on pelvic phantoms. Both used the difference between the intraoperative cup orientation, as displayed by the navigation system and the postoperative cup position, measured on computer tomography (CT) data. The CT measurements used the same reference system as the navigation system. RESULTS: The intraobserver measurement variability ranged from 48.4 degrees to 49.5 degrees for cup abduction and from 12 degrees to 13.5 degrees for anteversion. The interobserver variability ranged from 47.5 degrees to 19 degrees for cup abduction and from 11.8 degrees to 13.8 degrees for anteversion. Overall errors were calculated for cup abduction and anteversion. Cup navigation was accurate on pelvic bone phantoms. The anteversion error ranged from 0 degrees to 2.5 degrees (mean 0.9 degrees, standard deviation 0.7 degrees). For the clinical study, abduction errors ranged from 2.1 degrees to 16.7 degrees. The mean abduction error introduced by the acquisition of anatomic landmarks was 7.2 degrees. DISCUSSION: The proposed simple clinical end-to-end accuracy evaluation model provides the surgeon with sufficiently accurate information. The evaluation model was able to identify and more importantly to quantify the clinically induced error. This study proves that ameliorating the reference system acquisition would improve the system's overall accuracy.

Modeling the impact of prostate edema on LDR brachytherapy: a Monte Carlo dosimetry study based on a 3D biphasic finite element biomechanical model.

Prostate volume changes due to edema occurrence during transperineal permanent brachytherapy should be taken under consideration to ensure optimal dose delivery. Available edema models, based on prostate volume observations, face several limitations. Therefore, patient-specific models need to be developed to accurately account for the impact of edema. In this study we present a biomechanical model developed to reproduce edema resolution patterns documented in the literature. Using the biphasic mixture theory and finite element analysis, the proposed model takes into consideration the mechanical properties of the pubic area tissues in the evolution of prostate edema. The model's computed deformations are incorporated in a Monte Carlo simulation to investigate their effect on post-operative dosimetry. The comparison of Day1 and Day30 dosimetry results demonstrates the capability of the proposed model for patient-specific dosimetry improvements, considering the edema dynamics. The proposed model shows excellent ability to reproduce previously described edema resolution patterns and was validated based on previous findings. According to our results, for a prostate volume increase of 10-20% the Day30 urethra D10 dose metric is higher by 4.2%-10.5% compared to the Day1 value. The introduction of the edema dynamics in Day30 dosimetry shows a significant global dose overestimation identified on the conventional static Day30 dosimetry. In conclusion, the proposed edema biomechanical model can improve the treatment planning of transperineal permanent brachytherapy accounting for post-implant dose alterations during the planning procedure.

Towards a realistic echographic simulator.

Echography is a useful tool to diagnose a thrombosis; however, since it is difficult to learn to perform this procedure, the objective of this work is to create a simulation to allow students to practice in a virtual environment. Firstly, a physical model of the thigh was constructed based on experimental data obtained using a force sensor mounted on a robotic arm. We present a spring damper model consisting of both linear and non-linear elements. The parameters of each of these elements are then fitted to the experimental data using an optimization technique. By employing an implicit integration to solve the dynamics of the system we obtain a stable physical simulation at over 100 Hz. Secondly, a haptic interface was added to interact with the simulation. Using a PHANToM force-feedback device may touch and deform the thigh in real-time. In order to allow a realistic sensation of the contact we employ a local modeling technique allowing to approximate the forces at much higher frequency using a multi-threaded architecture. Finally, we present the basis for a fast echographic image generation depending on the position and orientation of the virtual probe as well as the force applied to it.

Pre- and intra-irradiation multimodal image registration: principles and first experiments.

Accurately repositioning the patient with respect to CT or MR images is essential for high precision radiotherapy. We show that portal images may be automatically registered with 3D pre-session data (typically morphological images like CT or MR images), thus enabling an automatic adjustment of the planned strategy to the actual position of the patient. Based on computer vision techniques, the principles of this new method of multimodal image registration are presented, and the first experiments with a phantom are analysed.

Conformal external radiotherapy of prostatic carcinoma: requirements and experimental results.

The aim of conformal radiotherapy is to deliver, with high precision, a specific dose (which may be a high dose) to a planning target volume, concurrently with irradiating as little as possible healthy tissue and organs at risk. Radiation therapy may suffer from a number of problems that result in both over- or under-sizing the irradiation fields, making over-rough simplifications of the irradiation ballistics and delivering an insufficient tumoral dose (to spare critical organs and reduce toxicity). One of these problems lies in the accurate positioning of the planning target volume with respect to the irradiation system, thence in the correct execution of the ballistics. In this paper, we describe a system aiming at achieving a higher overall accuracy in the delivery of prostatic boost for carcinoma of the prostate. The system is based on the use of ultrasonic images for measuring the actual position of the prostate just before irradiation. Since these images are registered with pre-operative (CT or MR) images, the position and orientation of the planning target volume is computed with respect to the irradiation system, and can be corrected accordingly. First experiments have been performed on dummies, and the results are discussed.

Guiding systems for computer-assisted surgery: introducing synergistic devices and discussing the different approaches.

Computer-assisted surgery (CAS) or computer-assisted therapy (CAT) attempt primarily to optimize the performance of medical tasks. CAS systems include a guiding system to connect the information world of data and plans to the physical world of surgeons, patients and instruments, and to supplement the surgeon's perception and dexterity. Passive, semi-active and active systems have been proposed and implemented in various clinical applications. In this paper we introduce synergistic devices which are an extension of semi-active systems. We also discuss the advantages of the different categories of guiding systems on the basis of a list of task-oriented and user-oriented qualitative factors.

Model driven therapy - the instance of computer assisted medical interventions.

OBJECTIVES: Taking into account a priori knowledge is a key issue to meet the medical, scientific and industrial challenges of the progresses of Minimally Invasive Surgery. We propose an overview of these challenges. METHODS: Models play a major role in representing the relevant knowledge to plan and realize complex medical and surgical interventions. We analyze the three basic steps of Perception, Decision and Action, and illustrate by some instances how models may be integrated in these steps. RESULTS: We propose a selection of the results obtained in Model Driven Therapy. These results illustrate the issues of Perception (models allow accurate reconstruction of 3D objects from a limited set of X-ray projections), Decision (models allow to take into account elastic and dynamic characteristics of muscles), and Action (models allow to design innovative navigational and robotics aids to the realization of complex interventions). Likewise, models play a major role in the process of surgeon's education, which leads to the concept of Virtual Orthopedic University. CONCLUSIONS: Model Driven Therapy emerges as the way to perform optimal medical and surgical interventions, providing physicians and surgeons with the possibility to augment their capacities of sensing multi-modal information, of combining them to define optimal strategies, and of performing accurate and safe actions.

[3-D conformal radiotherapy procedure and registration of pre- and intra-radiotherapeutic data]. / Procédure de la radiothérapie conformative tridimensionnelle et mise en correspondance des données pré- et per-radiothérapiques.

The authors describe the different steps of 3-D conformal external irradiation. They mention as well two procedures of isocentric repositioning which are mandatory for the matching of anatomical data: the first one is acquired before the simulation and the second one just before the radiotherapy session.

Accurate guidance for percutaneous access to a specific target in soft tissues: preclinical study of computer-assisted pericardiocentesis.

In the field of percutaneous access to soft tissues, our project was to improve classical pericardiocentesis by performing accurate guidance to a selected target, according to a model of the pericardial effusion acquired through three-dimensional (3D) data recording. Required hardware is an echocardiographic device and a needle, both linked to a 3D localizer, and a computer. After acquiring echographic data, a modeling procedure allows definition of the optimal puncture strategy, taking into consideration the mobility of the heart, by determining a stable region, whatever the period of the cardiac cycle. A passive guidance system is then used to reach the planned target accurately, generally a site in the middle of the stable region. After validation on a dynamic phantom and a feasibility study in dogs, an accuracy and reliability analysis protocol was realized on pigs with experimental pericardial effusion. Ten consecutive successful punctures using various trajectories were performed on eight pigs. Nonbloody liquid was collected from pericardial effusions in the stable region (5 to 9 mm wide) within 10 to 15 minutes from echographic acquisition to drainage. Accuracy of at least 2.5 mm was demonstrated. This study demonstrates the feasibility of computer-assisted pericardiocentesis. Beyond the simple improvement of the current technique, this method could be a new way to reach the heart or a new tool for percutaneous access and image-guided puncture of soft tissues. Further investigation will be necessary before routine human application.

[Image fusion methods for the repositioning of the patient in radiotherapy]. / Méthodes de recalage d'images pour le repositionnement de patients en radiothérapie.

Conformal radiotherapy requires the accurate and reproducible setup of the patient for each fraction delivery. Megavoltage imaging could enable this. This requires the development of image processing and data fusion algorithms. We describe an automated method based on the use of mutual information for registration. Such a method does not require any preliminary segmentation of the images. This method has been extensively tested on phantom as well as on some patient data. The obtained results demonstrated that this automated method for 2D/2D registration is rapid, accurate and robust even in the case of blurred images for small treatment fields.

The use of a semi-customized phantom for verification of conformal plans.

We have developed a technique for inverse treatment planning of prostate therapy designed to improve the degree of conformation between the dose distribution and the target volume. We compared the inverse plan with a "standard" four-field box technique as well as a four-field technique using oblique fields ("cross technique"). We validated the dosimetry of the inverse plan using Fricke gel solution in phantom specifically designed for this purpose. The phantom is a Plexiglas tank with a cross section, which approximates the dimensions of the pelvis. Anatomical data from computed tomography (CT) images of a patient were used to simulate organs in our phantom. This allows us to calculate dose distributions with the external geometry of the phantom and internal anatomy of the patient. Dose-volume histograms (DVHs) for the three different plans were calculated. The phantom containing the Fricke gel was irradiated according to the inverse plan. Magnetic resonance (MR) images was used to determine the dose distribution delivered to the phantom. We observe, on DVHs, that the inverse plan significantly reduces the dose to the rectum and the bladder but slightly increases the inhomogeneity inside the target volume. Correlation is good between isodoses on MR images and calculated isodoses. We conclude that inverse planning software can greatly improve the conformal degree of treatment to the prostate. This technique could be applied to other complex anatomic sites at which dose to organs at risk is a limiting factor and increased dose to the target volume is indicated. Our phantom and the Fricke gel solution are convenient to carry out validation of conformal treatments.

Building a hybrid patient's model for augmented reality in surgery: a registration problem.

In the field of Augmented Reality in Surgery, building a hybrid patient's model, i.e. merging all the data and systems available for a given application, is a difficult but crucial technical problem. The purpose is to merge all the data that constitute the patient model with the reality of the surgery, i.e. the surgical tools and feedback devices. In this paper, we first develop this concept, we show that this construction comes to a problem of registration between various sensor data, and we detail a general framework of registration. The state of the art in this domain is presented. Finally, we show results that we have obtained using a method which is based on the use of anatomical reference surfaces. We show that in many clinical cases, registration is only possible through the use of internal patient structures.

A six-degree-of-freedom passive arm with dynamic constraints (PADyC) for cardiac surgery application: preliminary experiments.

The purpose of Computer-Assisted Surgery (CAS) is to help physicians and surgeons plan and execute optimal strategies from multimodal image data. The execution of such planned strategies may be assisted by guidance systems. Some of these systems, called synergistic systems, are based on the cooperation of a robotic device with a human operator. We have developed such a synergistic device: PADyC (Passive Arm with Dynamic Constraints). The basic principle of PADyC is to have a manually actuated arm that dynamically constrains the authorized motions of the surgical tool held by the human operator during a planned task. Dynamic constraints are computed from the task definition, and are implemented by a patented mechanical system. In this paper, we first introduce synergistic systems and then focus on modeling and algorithmic issues related to the dynamic constraints. Finally, we describe a 6-degree-of-freedom prototype robot designed for a clinical application (cardiac surgery) and report on preliminary experiments to date. The experimental results are then discussed, and future work is proposed.

Clinical results of percutaneous pelvic surgery. Computer assisted surgery using ultrasound compared to standard fluoroscopy.

This study presents early results of clinical experience with the application of Computer Assisted Surgery (CAS) to percutaneous iliosacral screwing, with comparison to a historical series of patients treated using percutaneous fluoroscopy. Four patients were instrumented using a CAS system, with 10 screws being inserted. Thirty patients were treated by percutaneous fluoroscopic screwing, with 51 screws being inserted. The follow-up assessment included the following criteria; operative time, parameters of radiation exposure, neurological examination, screw placement evaluation on CT-scan, antalgic drug consumption, pain, Majeed grading, and loosening of implants. In the CAS group, the average radiation time was 0.35 min per patient and 0.14 min per screw. No trajectories outside the bone and no postoperative neurological deficits were found. In the fluoroscopic group, the average radiation time was 1.03 min per patient and 0.6 min per screw. Twelve screws had outside-bone trajectories, and iatrogenic neurological deficits were found in seven patients. The average operative time was 50 min in the CAS group and 35 min in the fluoroscopic group. The present CAS technique shows better placement of iliosacral screws, with no outside-bone trajectories and lower radiation exposure.

Bone morphing: 3D morphological data for total knee arthroplasty.

OBJECTIVE: The clinical outcome of a total knee arthroplasty (TKA) is mainly determined by the accuracy of the surgical procedure itself. To improve the final result, one must take into account (a) the alignment of the prosthesis with respect to the mechanical axis, and (b) the balance of the soft tissues. Therefore, morphologic data (such as the shape of the epiphysis) and geometric data are essential. We present a new method for performing TKA based on morphologic and geometric data without preoperative images. MATERIALS AND METHODS: The global method is based on the digitization of points with an optical 3D localizer. For the morphologic acquisitions, we use a method based on the registration of sparse point data with a 3D statistical deformable model. To build the mechanical axis, we use a kinematics method for the hip center and digitization of anatomical landmarks for the ankle centers. The knee center is not determined by digitization or kinematics of the knee, as this would not be accurate. The surgical planning relies totally on the soft-tissue balance, which is the key issue for a good kinematics result. RESULTS: We have used this system for 6 months in a randomized clinical trial involving 35 patients to date. For the first 11 patients that could be measured in the navigation group, the postoperative frontal alignment was within the range of 180 +/- 3 degrees. Fluoroscopic assessment of the soft-tissue balancing will be performed at the conclusion of an extended 2-year study to evaluate the results from a functional point of view. CONCLUSION: Bone Morphing is an accurate, fast, and user-friendly method that can provide morphologic as well as geometric data. We have introduced the important notion of soft-tissue balancing into the intraoperative planning step to optimize the kinematics as well as the anatomy. Therefore, this method should be considered as an alternative to the CT-based method.

Computer assisted pericardial puncture: work in progress.

Until now, computer assisted surgery has focused primarily on surgical procedures involving rigid anatomical structures. Because soft tissues can be highly mobile and deformable, they may require specific imaging devices, suitable modeling tools, and guiding systems. Percutaneous pericardial puncture is a good clinical target for computer assisted surgery; this procedure is often performed without direct visualization and is dangerous even though echographic control is used. Computer assistance can greatly improve this technique and will allow accurate puncture of preplanned targets. This paper describes a new approach for computer assisted pericardial punctures (CASPER) and describes a first feasibility analysis of CASPER demonstrated with anesthetized animals. The approach is based on the use of echographic data localized in space, from which an optimal strategy is defined. Because of the specificity of the pericardial effusion, a stable target can be selected despite the heart motions. A passive guiding system is used. We have demonstrated the feasibility of the approach.