Dosimeter Checks Radiation Levels in Tooth Enamel

The newest version of the device weighs about 25 kilograms, but an older, larger dosimeter, weighing about a ton and a half, is already in Japan. To measure radiation levels, the patient bites down on a mouthpiece and rests his head against some padding to remain still; an antenna helps to hold the lips away from the device.

EPR spectroscopy technology is based on the fact that ionizing radiation generates large numbers of unpaired electron species in irradiated materials, including biologic tissues, and especially in calcified tissues. These free electrons are captured, creating carbonate radical centers. Since in the natural formation of teeth, carbonate ions are incorporated into biological hydroxyapatite during mineralization (where they substitute for phosphate and hydroxyl ions), the radicals generated in tooth enamel are very stable, persisting indefinitely at levels that are directly proportional to dose.

"Testing enamel is a reliable way of measuring radiation exposure,” said Ben Williams, MD, of the Dartmouth-Hitchcock Medical Center (DHMC; Lebanon, NH, USA). "The changes in the tooth enamel caused by radiation are permanent. They don't change over time. So that allows us to make these measurements at any time after the exposure.”

"I don't think anyone quite recognized that modern reactors in a well-developed country like Japan also present a parallel risk. This has been mind-boggling what's happened in Japan,” added device developer Harold Swartz, MD, a professor of medicine and radiology at Dartmouth. "If you said to people in Japan outside the exclusion area 'If you have concerns that you received high doses of radiation, we will measure you,' I would guess you would get tens of thousands of people.”

Conventional EPR dosimetry involves the isolation of tooth enamel from extracted teeth, with measurements made at the X-band (~10 GHz bandwith). Measurements are compared to a universal calibration curve, or calibrated per the addition of several known doses. While this technique is well suited for use in limited populations following certain exposures, its use as a tool to perform screening after a large number of people have potentially been exposed to clinically relevant doses is limited by the need to extract a tooth and process it remotely at a specialized laboratory.

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