High-speed Automatic Frequency Controller for Tomotherapy Machine

High-speed Automatic Frequency Controller for Tomotherapy Machine

Circaflex is thrilled to have successfully built a control module for one of the most exciting technologies in cancer treatment of our century. Tomotherapy involves the targeted use of high energy gamma rays to fire photons directly into tumors to kill cancer cells without harming surrounding tissue.

WIthin a Tomotherapy device is a X-Ray generator that operates at several thousand pulses per second, and each pulse can be controlled in power, frequency, and focus to create a controlled beam of energy.

The customer approached Cyth with no time to spare to create a Automated Frequency Controller (AFC) to monitor each pulse and determine if the signal was on target, and output signals to a master controller. But since pulses arrived at 40 Kilohertz rates, we need to analyze them with a MegaHertz signal in order to monitor the behavior of the pulse. With a pulse arriving every 250us, with a pulse duration of only 400 us which we needed to digitize with about 1000 pulses, this requires an Analog voltage measurement greater than 400ns per sample, which is an acquisition rate approaching 2MS/s.

The best choice for the operation was the National Instruments Single-Board RIO (sbRIO) using Cyth's Circaflex mezzanine boards, which come with all the inputs and outputs the application needed except one - the MHz Analog Input (Analog-to-Digital conversion or ADC) for monitoring the pulse behavior.

With no more than 10 weeks to complete the project, Cyth used the first 5 weeks to deliver an evaluation unit with just 100 Kilo-sample per second (kS/s) Analog Input which was useful for testing but was not the final intended system. This unit implemented the second most critical feature which was two TCP/IP communication channels. The first channel was for commands and responses, while the second was for data streaming. This allowed the team to continue integration while the Analog Input was upgraded.

The next challenge was to upgrade the Analog Input to 2 MS/s, which was enough to provide the samples we need. Circaflex was able to rise to the challenge. Cyth answered the challenge by creating the new Circaflex 572 board for use on the sbRIO-9606, which provided the Analog Input required as well as the other forms of triggering, input, and output which would get the job done. Along with some customized packaging and mounting, the system was delivered onsite and integrated during a 2-day visit.

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