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More-Accurate Radiation Therapy

Small, implantable devices could measure radiation from within tumors themselves.

A simple wireless device implanted into tumors could give clinicians a more accurate indication of the amount of radiation that the tumors receive during treatment. The device, under development by engineers at Purdue University, is meant to assist doctors in precisely targeting radiation to tumors without hitting surrounding tissue.

Narrow gauge: A glass-encapsulated implantable device (shown protruding from the bore of a large surgical needle) can give doctors an exact indication of how much radiation tumors receive during treatment.

The device is encased in a capsule about 2.5 millimeters in diameter and two centimeters long–small enough to be injected into the body by a large syringe. It is a simple version of a dosimeter, an instrument for measuring radiation that is used to track the exposure of workers in high-risk areas. It contains a wire coil and a capacitor that can store an electric charge; together they form a circuit that has a particular electromagnetic resonance frequency. When exposed to radiation, the capacitor’s charge gradually dissipates, and the resulting change in frequency can be detected by an antenna placed outside the body.

“It measures the cumulative dose that the patient has received at each stage” of treatment, says Babak Ziaie, an engineer at Purdue who led the development of the device. After many exposures to radiation, the capacitor’s charge is depleted, so the device would be used during a single treatment regimen that spanned several weeks.

A similar device, called a dose verification system (DVS), has recently been developed by Sicel Technologies and approved for use in treating breast and prostate cancer. Ziaie believes that the simplicity of the Purdue device gives it an advantage over Sicel’s, which uses more-complicated electronic components. “The advantage of our system is that it’s very simple,” he says. “There are no electronics, no chip inside.” As a result, the device is easier to manufacture, and thus much cheaper to produce.

Radiation therapy is one of the most common treatments for cancer and is often used in combination with surgery or chemotherapy. It requires directing high-energy beams at cancerous tissue while avoiding healthy tissue. Both the Purdue and Sicel devices are intended as quality-control measures during radiation treatment of solid tumors such as prostate, breast, or lung cancers.

Arthur Ko, a radiation oncologist at Indiana University School of Medicine, says that “right now, when we deliver radiation, there is no way for us to measure what kind of dose is delivered exactly” to the tumor. Usually, several beams are combined to deliver a high amount of radiation to the target site. Before the procedure, Ko says, oncologists do a simulation to measure the combined effect of the beams. But an implantable device would allow clinicians to verify the dosage at the actual site. He believes that having such a readout “could potentially change the way we deliver radiation.”

Joel Tepper, a radiation oncologist at the University of North Carolina School of Medicine, says that radiation delivery techniques are actually very good at concentrating radiation at a specific point in space, but that “getting the patient in the right spot all the time is a big issue.” While MRI and other imaging techniques can locate a tumor before treatment, the patient’s anatomy can shift slightly over time, making it difficult to ensure that the radiation is hitting the tumor precisely. An implantable dosimeter located at the tumor site could help solve this problem, but Tepper is not sure that the idea will catch on with clinical oncologists. “It’s not clear right now to me precisely what the major impact of these would be,” Tepper says. But he adds that if the devices become very tiny and inexpensive or combine multiple functions, they could prove to be more useful.

A smaller device would allow clinicians to gauge the amount of radiation delivered to specific sites more accurately. Ziaie’s team is now working to halve the size of its device, and to combine it with a magnetic tracking system that would simultaneously give doctors information about the location of the tumor. Ziaie hopes to begin testing the device in animals by the end of the year and in patients in the next two years.

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