Implantable wireless device for measuring radiation dose in tumours
19 April 2006
West Lafayette, Ind. USA. Engineers at Purdue University are creating a
wireless device the size of a rice grain that could be implanted in tumours
to tell doctors the precise dose of radiation received and locate the exact
position of tumours during treatment.
engineer Babak Ziaie shows the prototype wireless device he has
developed with doctoral student Chulwoo Son at the University's
Birck Nanotechnology Center. (Purdue News Service photo/David
Researchers at Purdue's Birck Nanotechnology Center have tested a
dime-size prototype to prove the concept and expect to have the miniature
version completed by the end of summer, said Babak Ziaie (pronounced
Zee-Eye-Eee), an associate professor in the School of Electrical and
"Currently, there is no way of knowing the exact dose of radiation
received by a tumour," Ziaie said. "And, because most organs shift inside
the body depending on whether a patient is sitting or lying down, for
example, the tumour also shifts. This technology will allow doctors to
pinpoint the exact position of the tumour to more effectively administer
The device is a passive wireless transponder, which has no batteries
andis activated with electrical coils placed next to the body. "It will be
like a capsule placed into the tumour with a needle," said Ziaie, who has a
dual appointment in Purdue's Weldon School of Biomedical Engineering.
Although imaging systems now used can provide a three-dimensional fix on
a tumour's shifting position during therapy, these methods are not easy to
use during radiation therapy, are costly and sometimes require X-rays, which
can damage tissue when used repeatedly, he said. Doctors could use the
wireless technology, however, to precisely track a tumour by using three or
six coils placed around the body to pinpoint the location of the electronic
device, Ziaie said.
Researchers tested the prototype with a radioactive caesium. The device,
which contains a miniature version of dosimeters worn by people in
occupations involving radioactivity, could provide up-to-date information
about the cumulative dose a tumour is receiving over time.
The technology uses the same principle as electret microphones, popular
products found in consumer electronics stores. The 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 slightly, increasing and decreasing the capacitance and altering the
flow of electric current through the circuit, creating a signal that
transmits information stored in the dosimeter.
"It's basically like a very small tuning circuit in your radio," Ziaie
said. "This will be a radiation dosimeter plus a tracking device in the same
capsule. It will be hermetically sealed so that it will not have to be
removed from the body."
The device is an example of a microelectromechanical system, or a tiny
mechanical device fabricated using methods generally associated with
microelectronics. The Purdue engineers have begun working with researchers
at the Indiana University School of Medicine to further develop the
The research has been funded by the National Science Foundation. Research
findings were published in the proceedings of the 19th IEEE International
Conference on Micro Electro Mechanical Systems, a conference organized by
the Institute of Electrical and Electronics Engineers.