The radiation issue in cardiology: the time for action is now

Abstract

The "radiation issue" is the need to consider possible deterministic effects (e.g., skin injuries) and long-term cancer risks due to ionizing radiation in the risk-benefit assessment of diagnostic or therapeutic testing. Although there are currently no data showing that high-dose medical studies have actually increased the incidence of cancer, the "linear-no threshold" model in radioprotection assumes that no safe dose exists; all doses add up in determining cancer risks; and the risk increases linearly with increasing radiation dose. The possibility of deterministic effects should also be considered when skin or lens doses may be over the threshold. Cardiologists have a special mission to avoid unjustified or non-optimized use of radiation, since they are responsible for 45% of the entire cumulative effective dose of 3.0 mSv (similar to the radiological risk of 150 chest x-rays) per head per year to the US population from all medical sources except radiotherapy. In addition, interventional cardiologists have an exposure per head per year two to three times higher than that of radiologists. The most active and experienced interventional cardiologists in high volume cath labs have an annual exposure equivalent to around 5 mSv per head and a professional lifetime attributable to excess cancer risk on the order of magnitude of 1 in 100. Cardiologists are the contemporary radiologists but sometimes imperfectly aware of the radiological dose of the examination they prescribe or practice, which can range from the equivalent of 1-60 mSv around a reference dose average of 10-15 mSv for a percutaneous coronary intervention, a cardiac radiofrequency ablation, a multi-detector coronary angiography, or a myocardial perfusion imaging scintigraphy. A good cardiologist cannot be afraid of life-saving radiation, but must be afraid of radiation unawareness and negligence.

Figures

Figure 1

Medical and natural sources of radiation. Modified from Picano E, BMJ, 2004, ref. 2 updated with Mettler et al, Health Physics, 2009, ref. 16. The effective dose of 1 mSv is equivalent to 50 chest x-rays.

Figure 2

The relative contribution of cardiovascular examinations to overall exposure from nuclear medicine (left panel) referred to radiological years 2006. The nuclear cardiology contribution of about 32 chest x-rays per year is matched by the 33 chest x-rays per year from cardiac radiology, for a grand total of 65 chest x-rays, corresponding to 43% of the total exposure of the average US citizen. Redrawn and adapted from ref 16 and 17.

Figure 3

The risk model of Biological Effects of Ionising Radiation Committee VII for exposure to low-level radiation predicts that about one (red star) out of 100 people would likely develop solid cancer or leukemia from a single exposure of 100 mSv above background. About 42 additional people (yellow circles) in the same group would be expected to develop solid cancer or leukemia from other causes in a lifetime. Roughly half of these cancers would result in death. Modified and adapted from Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation; Nuclear and Radiation Studies Board, Division on Earth and Life Studies, National Research Council of the National Academies. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. Washington, DC: The National Academies Press; 2006 (ref. [8]

Figure 4

The population risk is in reality due to the average of a spectrum of risks, with higher risks being for instance associated with mutation of genes involved in DNA repair and with the presence of other environmental mutagens such as smoking.

Figure 5

The radiological dose-sparing cascade provided by technical and cultural upgrading in four critical areas of cardiology: Myocardial Perfusion Imaging (MPI, from thallium to sestamibi tracers, from standard to triple-headed gamma camera, and from gamma camera to PET imaging with N-13 ammonia), MDCT (Multi-Detector Computed Tomography, from retrospective to prospective triggered techniques with dose modulation), interventional cardiology (with 90% dose reduction simply achieved through radioprotection training) and cardiac radiofrequency ablation (moving from standard fluoroscopy to near-zero exposure with non-fluoroscopy navigation techniques).

Figure 6

The dose-effect relationship between radiation exposure and cancer. The solid line indicates the epidemiological evidence, which is conclusive for doses above 50 to 100 mSv. The dashed line indicates the dose range with absent or inconclusive evidence.