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Nuclear imaging, CT accounted for bulk of radiation dose from imaging procedures
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Imaging procedures were a source of exposure to doses of ionizing radiation, which tended to become cumulative over time.
Using claims data from UnitedHealthcare, researchers for the retrospective study included 952,420 patients in the cohort. Among those, 655,613 (68.8%) were exposed to radiation during imaging procedures within the three-year study period. A mean of 1.2 procedures per person per year and a median of 0.7 procedures per person per year were reported. The largest proportion of patients came from the Dallas-area market (n=298,747), and the smallest proportion was from the Orlando-area market (n=133,561).
According to the study results, the mean effective dose of radiation administered to the patients was 2.4 mSv per person per year, with a median effective dose of 0.1 mSv per person per year. The proportion of patients undergoing imaging procedures was higher among older patients compared with younger patients (49.5% vs. 85.9%), and women had more imaging procedures than men (78.7% vs. 57.9%).
Moderate effective doses of radiation were incurred annually in 193.8 patients per 1,000; high doses in 18.6 patients per 1,000; and very high doses in 1.9 patients per 1,000. CT and nuclear imaging accounted for 21% of the total procedures and 75.4% of the total effective radiation dose. By contrast, procedures related to plain radiography accounted for 71.4% of the total number of procedures but accounted for only 10.6% of the total effective radiation dose. Most of the total effective radiation dose was delivered in the outpatient setting (81.8%).
Fazel R. N Engl J Med. 2009;361:849-857.
This article has high visibility and high impact, but follows on the heels of many efforts to reduce radiation exposure. ‘Imaging gently’ has become the mantra of radiology, nuclear medicine and cardiology based on several such publications drawing attention to medical radiation exposure. In CT angiography, we now routinely do axial scanning (not helical scanning) with prospective electrocardiogram triggering (not retrospective ECG gating) for a brief fraction of the heart beat’s cycle (not the entire cardiac cycle), resulting in about a fivefold reduction in radiation exposure. In nuclear cardiology, we have stopped the routine use of dual-isotope (thallium-201 at rest and technetium-99m (Tc-99m)-tetrofosmin or -sestamibi at stress) imaging and use low-dose or high-dose Tc-99m perfusion agents. This results in a drop from 26 mSv of radiation exposure for dual-isotope to 9 mSv for tetrofosmin or 11 mSv for Tc-99m-sestamibi. In addition, there are newer protocols using stress imaging alone, as well as lower-than-usual tracer doses with faster cameras and resolution recovery software.
In summation, they are sounding the fire alarm after the fire department has arrived, but the fire is not yet extinguished. We have been all over this issue for the past two years and will continue to develop ways of getting the same excellent clinical information with reduced exposure.
– Kim A. Williams, MD
Cardiology Today Editorial Board member