One of the problems with radiation therapy is determining how much radiation a tumor has received compared to the assigned dose.

But now engineers at Purdue University (West Lafayette, Indiana) are creating a wireless device the size of a grain of rice that could be implanted in tumors to tell doctors the precise dose of radiation received and to locate the exact position of these tumors during treatment. The researchers at Purdue's Birck Nanotechnology Center have tested a dime-sized prototype to prove the concept and are aiming to have the miniaturized prototype completed by the end of summer.

The research findings were detailed in a paper that appeared earlier this year in proceedings of the IEEE International Conference on Micro Electro Mechanical Systems, a conference organized by the Institute of Electrical and Electronics Engineers (IEEE; New York).

"There is a great need, and the application is really important," Babak Ziaie, PhD, an associate professor in the School of Electrical and Computer Engineering, told Diagnostics & Imaging Week, noting that, until now, there has been no way of precisely measuring radiation dose in radiation therapy.

That being said, Ziaie acknowledged being aware of another development in the area.

The report of Ziaie's work by Purdue comes on the heels of last week's announcement by Sicel Technologies (Raleigh, North Carolina) that it had received FDA 510(k) clearance for its Dose Verification System, a wireless implantable radiation sensor and reader designed to help radiation oncologists determine dosage. The device also provides physicians with the knowledge of how much radiation has hit the target.

At this point, Sicel's DVS sensor is approved only for breast cancer, but the company said it expects to expand the indications for radiation treatment of other cancers.

Ziaie said the Purdue device is differentiated by being a "passive" device, i.e., a "passive wireless transponder" which has no batteries and will be activated with electrical coils placed next to the body, whereas the Sicel device is an "active" device.

"It will be like a capsule placed into the tumor with a needle," said Ziaie, who has a dual appointment in Purdue's Weldon School of Biomedical Engineering.

"You basically bring a coil next to the body from outside, and you interrogate the device, which is the rice grain inside [the body]," said Ziaie. "And inside the device you have a miniature coil, and a capacitor inside. That's it; we don't have anything else."

According to Purdue, the technology uses the same principle as an electret microphone, which is, according to, a name that comes from "electrostatic and magnet." Electret microphones contain a membrane that vibrates in response to sound waves. Between the membrane and a metal plate is an air gap that serves as a capacitor, or a device that stores electricity. As the membrane vibrates, the size of the air gap changes, increasing and decreasing, thus altering the flow of electric current through the circuit. That, in turn, creates a signal that transmits information, which in this case would be stored in the device.

Ziaie said the value of the capacitor changes as a function of how much radiation it receives, so "there is no resonant frequency of the device changes."

"From outside, you can track these resonant frequency changes," he said.

Purdue said that doctors could use the wireless technology also to precisely track a tumor by using three or six coils placed around the body to pinpoint the location of the electronic device.

The external device which reads signals from the implant will be more like a "pager device," Ziaie said, or "like maybe one of the larger cell phones that you can bring next to the body and read out basically."

Ziaie said that while there are companies interested in the technology, it will likely be one to two years before it is licensed. Until then, Ziaie will work with researchers at the Indiana School of Medicine (Indianapolis) to continue to develop the technology.

The National Science Foundation (Arlington, Virginia) provided about $200,000 in funding for the project. Going forward, Ziaie hopes to get funding from the National Institutes of Health (Bethesda, Maryland) to continue the project with both animal trials and clinical trials.