A telerobotic system designed to treat bladder cancer
03 April 2013
The basic method that doctors use to treat bladder cancer hasn’t changed much in 70 years. That may be about to change with new research into a robotic surgical device.
An interdisciplinary collaboration of engineers and doctors at Vanderbilt and Columbia Universities in the US, headed by Nabil Simaan, an associate professor of mechanical engineering at Vanderbilt, has developed a prototype telerobotic platform designed to be inserted through the urethra that can provide surgeons with a much better view of bladder tumours so they can diagnose them more accurately. It is also designed to make it easier to remove tumours from the lining of the bladder regardless of their location – an operation called transurethral recession.
“When I observed my first transurethral resection, I was amazed at how crude the instruments are and how much pushing and stretching of the patient’s body is required,” Simaan said.
That experience inspired the engineer to develop a system that uses micro-robotics to perform this difficult type of surgery. The specialised telerobotic system “doesn’t take the judgment out of surgeons’ hands, it enhances their capabilities and hopefully gives them surgical superpowers,” comments Duke Herrell, an associate professor of urologic surgery and biomedical engineering, who specialises in minimally invasive oncology at Vanderbilt University Medical Center and is collaborating on the project.
The traditional method, which Simaan observed, involves inserting a rigid tube called a resectoscope through the urethra and into the bladder. The instrument contains several channels that allow the circulation of fluid, provide access for an endoscope for observation and interchangeable cauterising tools used to obtain biopsy tissue for evaluating the malignancy of the tumour and to resect small tumours. In some operations, surgeons replace the cauterising tool with an optical-fibre laser to destroy tumour cells.
Although the endoscope can give a good view of the bladder lining directly across from the opening of the urethra, inspecting the other areas is more difficult. The medical team must press and twist the scope or push on the patient’s body to bring other areas into view. These contortions are also necessary when removing tumours in less accessible areas.
If the surgeon, using endoscopic observation or biopsy, determines that a tumour is invasive and has penetrated the muscle layer, then he later performs a cystectomy that removes the entire bladder through an incision in the abdomen. Frequently this is done using a normal surgical robot. But, when the surgeon judges that the tumour is superficial (restricted to the bladder lining) then he attempts to remove it using the resectoscope.
Bladder cancer is so expensive to treat in part because the tumours in the bladder lining are exceptionally persistent and so require continuing surveillance and repeated surgeries. Among the factors that contribute to this persistence is the difficulty of accurately identifying tumour margins and failure to remove all the cancerous cells.
“Because you are working through a long, rigid tube, this can be a difficult procedure, especially in some areas of the bladder,” said Herrell.
The telerobotic system is designed specifically to operate in this challenging environment. The machine itself is the size and shape of a large Thermos bottle but its business end is only 5.5mm in diameter and consists of a segmented robotic arm. The tiny arm can curve through 180 degrees, allowing it to point in every direction including directly back at its entry point. At the tip of the arm is a white light source, an optical fibre laser for cauterisation, a fibrescope for observation and a tiny forceps for gripping tissue.
The engineers report that they can control the position of the snake-like arm with sub-millimeter precision: a level adequate for operating in clinical conditions. They have also demonstrated that the device can remove tissue for biopsies by gripping target tissue with the forceps and then cutting it off with the laser.
The fibrescope produced a 10,000-pixel image that was directed to a digital video camera system. Because it is steerable, the instrument was able to provide close-up views of the bladder walls at favourable viewing angles. However, the testing revealed the camera system’s effectiveness was limited by poor distance resolution. According to the researchers, this can be corrected by re-designing the fibrescope or by replacing it with a miniature camera tip.
In the future, the researchers intend to incorporate additional imaging methods for improving the ability to identify tumour boundaries. These include a fluorescence endoscope, optical coherence tomography that uses infrared radiation to obtain micrometer-resolution images of tissue and ultrasound to augment the surgeon’s natural vision.
In addition to these observational methods, the researchers have given their robot arm a sense of touch. Using a technique called force-feedback, they can measure the force acting on the tip when it comes into contact with tissue. Normally, tumours protrude from the surrounding tissue. Vanderbilt doctoral candidate, Andrea Bajo used this fact to successfully design new algorithms that allow the robot arm in the device to accurately trace a tumour’s edge. He did so by positioning the tip on the edge of a tumour and instructing it to move in the direction that maintains the same pressure.
“Surgeons can typically identify the gross visual margin of a tumour within a millimetre, but a robot like this has the potential of doing so with sub-millimetric precision and additional technologies may actually be able to distinguish margins at the cellular level,” said Herrell.
The team plans to make use of this level of precision to program the robot to perform what surgeons call an 'en-block resection', the removal of an entire tumour plus a small margin of normal tissue in one operation. That procedure is designed to ensure that no cancerous cells are left behind that can reseed the tumour.
The engineers are also using the system’s capabilities to design a number of safety measures into the telerobotic system. For example, the operator can set a maximum depth that the laser will cut and, even if the operator’s hand slips, the robot will not cut any deeper.
These safety measures are an example of Simaan’s primary research goal: develop surgical robotic systems that can be inserted into the human body and interact safely with it.