Researchers will present the findings October 30, 2007, at the American Society for Therapeutic Radiology and Oncology annual meeting in Los Angeles. The Rochester study is among a number to result from a $21 million grant awarded in 2005 by the National Institutes of Health/National Institute of Allergy and Infectious Disease.

Investigators studied plasma cytokine changes and the expression of tissue biomarkers when adult and juvenile mice were exposed to a single low dose of external radiation between 0.5 and 10 gray, the unit of energy absorbed from ionizing radiation. The dose was designed to mimic the exposure from a dirty bomb. The tissue response of the younger mice indicated the radiation was more damaging, possibly causing long-term harm to the body's structure and function.

"It's difficult to think about developing strategies for a horrific, hypothetical event," said Jacqueline Williams, Ph.D., research associate professor of Radiation Oncology at the University of Rochester's James P. Wilmot Cancer Center. "But our work is teasing out some important nuances about how children and adults - and perhaps even the elderly - respond to exposure to radioactive particles. Our work could also apply to the clinical setting, as we learn how to better protect normal tissue from radiation exposure."

A dirty bomb is designed to leave behind a great amount of radioactive debris. Scientists believe that such a bomb would likely emit a combination of gamma, alpha and beta rays. That combination can destroy cells in the lungs and intestines, particularly when inhaled or ingested.

The next step is to study precisely how internal radioactive contamination might affect animals and humans. Exposure to inhaled radioactive particles is very different from exposure to external radiation exposure. When a person receives external radiation to treat cancer, for example, he or she does not become radioactive. The exposure stops once the therapeutic radiation beam is turned off.

But continuous exposure, internally, to radioactive particles is a potential health risk. In the event of an attack with a radioactive or dirty bomb, radioactive dust and particles would likely stay in the air and linger on the ground, and breathing in or eating the radioactive dust could lead to long-term contamination. After the 1986 Chernobyl nuclear power plant explosion, for example, children drank milk from cows that had ingested radioactive particles by grazing in contaminated fields. The radioactive material eventually caused cancer in many of those children, Williams said.

Although scientists have not studied much about the consequences of inhaled radioactive exposure since the Cold War ended, the government ramped up funding for this type of research after the Sept. 11, 2001 attacks. The University of Rochester was among several centers nationwide selected to improve the country's response to a radiological event.

Scientists are not sure why juvenile mice responded differently than adult mice to radiation exposure, and they are continuing that investigation.

Rochester researchers are also looking at ways to measure the original dose of radiation a person received, after the fact. Currently, doctors look for symptoms such as skin redness and vomiting in patients with suspected radiation poisoning. But those symptoms are vague and can be elicited by stress, William said. The Rochester study has focused on developing evidence such as biomarkers that could be used in a mass casualty event to assign treatment.

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