The risk of developing cancer due to radiation exposure from computed tomography and nuclear scans can be managed through careful radiation reduction techniques that are appropriate to each clinical situation, said Stephen Balter, Ph.D., in a presentation at Transcatheter Cardiovascular Therapeutics (TCT) 2009.

Although higher doses of radiation result in higher-quality images, Balter, of Columbia University Medical Center in New York, N.Y., said the risk of certain populations developing cancer increases along with the amount of radiation.

Balter examined data from the National Cancer Institute to illustrate the relationship between age and risk for developing future cancer. For example, in a 20-year-old female receiving an effective dose of 100 mSv, the risk for developing radiation-induced cancer was 1.65%, he said. The risk of the same 20-year-old female patient developing cancer within the next 20 years without the radiation exposure was 1.42%. Although the difference seems small, it translates to a substantial increase in risk, Balter said. Conversely, in a typical, 60-year-old male patient the same amount of radiation was associated with a rate of 0.49%, but the long-term risk for developing cancer without the radiation exposure was 27.71%, so the additional risk accompanying the radiation is quite small.

"As the population gets older, the natural incidence of radiation goes up and the radiation risks go down, and so the relative importance of radiation goes down," he said.

Balter cited data from a 2008 study suggesting that one chest X-ray yielded 0.02 mSv of radiation. The effective dose from a CT angiography scan was equivalent to about 800 chest X-rays, CT calcium scoring was equivalent to 150 chest X-rays, diagnostic cardiography was equivalent to 350 chest X-rays and angioplasty equivalent to 750 chest X-rays. Dual-isotope nuclear scans (40.7 mSv) were equivalent to 2,000 chest X-rays, while nuclear medicine scans using technetium-99 yielded a more moderate dose equivalent to 450 chest X-rays.

Balter highlighted 2006 data from the National Council on Radiation Protection suggesting that nearly half of the entire collective United States population's annual radiation dose comes from medical radiation generated during CT scans, nuclear medical scans, interventional fluoroscopy and conventional radiography/fluoroscopy. Dual-isotope nuclear scans tended to deliver higher effective radiation doses than CT angiography, CT imaging for calcium scoring and CT angiography scans.

Methods for radiation reduction depend on the modality, Dr. Balter explained. For fluoroscopy, radiation reduction could be accomplished with modification of the X-ray beam and lower frame rates. For CT, global reductions in beam intensity, beam-path modulation and the avoidance of primary breast irradiation have been cited as effective means for lowering radiation exposure. Techniques for lowering exposure from nuclear scans include clinically tailored protocols and patient-specific radionuclide administration.

"Radiation can be managed, but it has to be managed to fit the clinical situation," Balter concluded.