Tumors move during treatment, so they do not always receive the same dose of radiation. And oncologists need to know where tumors are so they can try to kill them using minimal radiation. Other imaging devices, such as MRIs and CAT scanners, can locate tumors but they are expensive, cumbersome during radiation treatment, and often expose patients to unnecessary radiation. So researchers at Purdue University developed a passive dosimeter small enough to be injected through a syringe and into a tumor. It consists of just coils and capacitors, no power source, and is about 2.5 mm in diameter and 2-cm long. Researchers hope to cut those dimensions in half so that the final devices will be about the size of a grain of rice.

In practice, doctors would inject the tracker into a tumor, then commence radiation treatment. Before subsequent treatments, they would use RFID technology to locate the device and, therefore, the tumor. And if the doctors were concerned, they could download data on how much radiation the tumor had received, information that should let them destroy the tumor quicker and with less radiation exposure to healthy tissues.

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