In 2001, I joined Calypso Medical as employee number 18. Our goal was to create a remarkable medical device that could track the location of the prostate to a millimeter of accuracy during prostate cancer treatments.
This level of accuracy is important because the prostate has a tendency to move unpredictably during normal bodily functions, like coughing, going to the bathroom, or passing gas. This makes it difficult to direct the radiation to the correct spot. Healthy tissue may accidentally receive the radiation, which can lead to increased side effects.
We called it GPS for the body. Rather than satellites whizzing around the earth to pinpoint your phone’s location, a sensor array the size of a pizza box hovers directly over the patient’s abdomen. This sensor communicates with three transponders, about the size of a grain of rice, that had been implanted in the prostate in an earlier procedure.
During treatment, the radiation technologist (RT) monitors the location of these transponders. If the prostate moves outside of the radiation beam, the RT is immediately alerted and can reposition the beam so that it is once again focused squarely on the tumor. If you know where the device is, you know where to target the radiation.
For this to work, we needed another system that could determine the location of the sensor array. Figuring out the best way to solve that problem was my job.
As is typical in small companies, everyone wore multiple hats. If I wanted to understand what was happening during treatment and how it would constrain my system, I would need to figure that out myself.
Luckily, a local hospital was very helpful and let me hang out with the RTs as they did their job. I watched how they aligned the patients and moved about the room and spoke with the medical physicists about how they calibrated and aligned the equipment. I needed to design my system to work with what was already happening. Ideally, it would be invisible to the RTs and patient.
After exploring several options, I settled on a ceiling mounted camera system that would see the array and could figure out its location. I used three cameras, even though two would be enough, so that the RTs could move about the room and not worry if they were blocking one of the cameras.
I developed simulations and was confident the system would work. But a prototype is much more convincing and can test errors in your assumptions that a simulation might miss.
I built the prototype with commercial-off-the-shelf tripods and cameras and software that I wrote. In testing we showed the concept worked even if you blocked a camera or the targets.
I then installed my prototype in an unused treatment space at the hospital, and we were able to simulate realistic usage. This work convinced the company leadership that I was on the right track.
Once everyone agreed that my concept would work, I was directed to select a partner to implement my concept in a way that would pass muster with the FDA.
The perfect partner would have certain features:
Not surprisingly, no such company existed.
One company had an FDA-approved camera-based solution, but the solution didn’t have the resolution we needed and wouldn’t work if someone walked in front of a camera. Any solution they created would have to be built from scratch.
Another company was a spin-off of a university in Munich, Germany. Their solution was technically solid, but they were a startup with no other customers and definitely not geographically desirable.
A third company had a technically solid solution and several customers in the movie business. They were a leading company for motion capture and had worked on movies like “The Hobbit”. Their location in California was not ideal, but at least they were in the same time zone and a single flight away.
The only missing element was that their device hadn’t been through an FDA approval process. We worked with a regulatory consultant and the company to develop an approach that worked for everyone. It’s been over 15 years, and this partner is still providing the camera system for the Calypso tracking system.
When designing a medical device, it’s critical that it works as it’s supposed to. The alternative can be the death of the patient. One of the tools that we used to accomplish this was failure mode and effects analysis (FMEA), a structured way to analyze how a product might fail and what you can do to prevent it. In this context, failure means the product doesn’t deliver the required performance, not that it stops working.
For instance, if your requirement is accuracy no worse than 1.0 mm and a condition results in a location err...
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