TCT
2009
The risk of developing cancer due to radiation exposure
from computed tomography and nuclear scans is dependent to a large extent on
the age and sex of the recipient.
According to a presentation by Stephen Balter,
PhD, of the Columbia
University Medical Center in New York, the doses of ionized radiation
emitted by different imaging modalities are important for the acquisition of
higher-quality images. Although higher doses of radiation result in
higher-quality images, the risk for developing cancer in certain populations
also increases with the amount of radiation received.
Relationship between age, sex, risk
Balter examined data
from the National Cancer
Institute to illustrate the relationship between age and the risk for
developing future cancer. Using a 20-year-old female receiving an effective
dose of 100 mSv as an example, Balter explained that the risk for developing
radiation-induced cancer was 1.65%. The risk for the 20-year-old female patient
developing cancer within the next 20 years without the radiation exposure was
similar at 1.42%, making the risk for radiation-induced cancer more substantial
for that patient. In a more typical, 60-year-old male patient, the same amount
of radiation yielded a risk closer to that of the 20-year-old female patient
(0.49%). The long-term risk for developing cancer absent the radiation
exposure, however, was 27.71%.
“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,” Balter said in his
presentation.
Citing 2006 data from the
National Council on
Radiation Protection and Measurements, Balter showed that nearly half of
the collective radiation dose in the United States dose results from medical
radiation generated during CT scans (24%), nuclear medical scans (12%),
interventional fluoroscopy (7%) and conventional radiography/fluoroscopy (5%).
Dual-isotope nuclear scans delivered higher effective radiation doses than CT
angiography, CT imaging for calcium scoring and CT angiography scans.
The radiation reduction techniques Balter highlighted
varied according to modality. For fluoroscopy, radiation reduction could be
accomplished with modification of the X-ray beam, lower frame rates and
collimation. For CT, global reductions in beam intensity, beam path modulation
and the avoidance of primary breast irradiation were cited as effective in
lowering radiation exposure. Techniques for lowering exposure in nuclear scans
included clinically tailored protocols and patient-specific radionuclide
administration.
Balter S. Session 1. Presented at:
Transcatheter
Cardiovascular Therapeutics 2009; Sept. 21-25, 2009; San Francisco.
