Radiation Exposure After Percutaneous Coronary Intervention: Is the Cancer Risk Real?

In modern-day medicine, several interventional procedures have been developed in the field of cardiovascular medicine and radiology. These procedures expose the patients to ionizing radiation. According to a United Nations report, interventional procedures constitute only 1% of radiation use in medicine, but contribute 10% of collective dose of radiation,¹ with an average dose of 10-300 mSv (milliSievert) per exposure, compared to 0.02 mSv per exposure for a chest x-ray.^2,3 Ionizing radiation can have deterministic effects (eg, injury to the skin) or non-deterministic (stochastic) effects (eg, cancer, heritable gene mutations). X-rays and gamma rays are sparsely ionizing electromagnetic rays and constitute low linear energy transfer (LET) radiation. The Biological Effects of Ionizing Radiation (BEIR) VIII risk model assumes a linear no threshold (LNT) risk model for stochastic effects after exposure to low LET radiation.² This means that risk of cancer increases proportionally to the dose of the radiation, with no low-dose threshold.⁴ At such low doses of exposure, the risk of developing cancer is naturally low, but not zero. 

The study by Godino et al⁵ in this month’s Journal of Invasive Cardiology estimated the cancer risk due to radiation exposure in patients undergoing percutaneous coronary intervention (PCI) for acute ST-elevation myocardial infarction (STEMI) and, at the other end of the spectrum, PCI for stable angina or reversible ischemia due to chronic total occlusion (CTO). The radiation dose was estimated using the indirect method of dose area product (DAP).⁶ Using standardized conversion factors and weights, equivalent and effective doses of radiation to each organ were estimated from DAP.^7,8 The effective dose was then incorporated into the BEIR VIII risk model² to estimate the long-term attributable risk (LAR) of cancer incidence in six organs: lungs, red bone marrow, skin, bone, thyroid, and colon.

There is no question that the immediate lifesaving benefit of PCI in STEMI patients far outweighs any long-term risks from radiation exposure during the procedure. Essentially, this study is about effects of radiation in those undergoing PCI for CTO. In general, the enthusiasm for doing PCI for chronic stable angina dwindled after the publication of the COURAGE trial results in 2007.⁹ The American College of Cardiology/American Heart Association 2011 guidelines¹⁰ recommend that “a PCI of CTO patient with appropriate clinical indications and suitable anatomy is reasonable.” “Appropriate” clinical indications include persistent angina and demonstration of large reversible ischemia on non-invasive imaging. Despite having collaterals, patients with CTO do not get enough blood supply in the area of the diseased vessel during times of increased demand. PCI for CTO resolves angina symptoms, improves exercise tolerance and left ventricular function, and reduces need for coronary artery bypass graft surgery.^11,12 Mortality benefit after PCI for CTO is questionable, with some studies showing benefit^13,14 and some showing none.¹⁵ CTO lesions are often complex, calcified, and hard to recanalize, resulting in frequent procedural failure and a longer intervention and fluoroscopy time,^11,16 leading to higher radiation exposure, which is illustrated in this study as well. 

At this time, there is insufficient evidence to defer a PCI procedure for a patient with CTO based on concerns for radiation exposure. The cancer risk estimation in this study was based on theoretical conjectures, which were mainly derived from observations of effects of radiation in survivors of Hiroshima/Nagasaki who were distant from the fallout and exposed to lower levels of radiation.³ These conjectures made many assumptions and were rife with inherent uncertainty. Actual epidemiologic data on the incidence of cancers attributable to the radiation exposure in this population were not available. While concern about radiation exposure following PCI for CTO is understandable, patients are frequently and repeatedly exposed to radiation during common radiologic tests like computerized tomography (CT) of chest and abdomen. Although a single CT scan does not deliver more than 10 mSv of radiation,^2,3 the frequency with which these tests are conducted in current clinical practice raises concerns about effects of cumulative exposure. There is a lack of current information and regulations regarding lifetime cumulative exposure to radiation from common radiologic procedures like CT scans. The potential benefits of a PCI for CTO are much more than the information derived from a CT scan. Hence, it is not possible to curtail PCI on the grounds of radiation exposure alone. On the other hand, as suggested by the authors, it is prudent to weigh the risk-benefit ratio in younger patients and take steps to minimize radiation exposure in the cardiac catheterization lab.

References

1. Pantos I, Patatoukas G, Katritsis DG, Efstathopoulos E. Patient radiation doses in interventional cardiology procedures. Curr Cardiol Rev. 2009;5(1):1-11.
2. Committee to Assess Health Risks from Exposure to Low Level of Ionizing Radiation. Health risks from exposure to low levels of ionizing radiation: BEIR VII phase 2: Washington, DC: National Academies; National Research Council.
3. Schneider JF. Report of the Council on Science and Public Health, subject: ionizing radiation exposure in the medical setting. CSAPH Report 2-A-06.
4. Einstein E, Henzlova M, Rajagopalan S. Estimating risk of cancer associated with radiation exposure from 64-slice computed tomography coronary angiography. JAMA. 2007;298(3):317-323.
5. Godina C, Maccagni D, Pavon AG, et al. Estimating organs cancer incidence related to patient radiation exposure following PCI for acute and chronic coronary total occlusion. J Invasive Cardiol. 2013;25(9):441-445. 
6. Jaco JW, Miller DL. Measuring and monitoring radiation dose during fluoroscopically guided procedures. Tech Vasc Interv Radiol. 2010;13(3):188-193.
7. Betsou S, Efstathopoulos E, Katritsis D, Faulkner K, Panayiotakis G. Patient radiation doses during cardiac catheterization procedures. Br J Radiol. 1998;71(846):634-639.
8. Compagnone G, Ortolani P, Domenichelli S, et al. Effective and equivalent organ doses in patients undergoing coronary angiography and percutaneous coronary interventions. Med Phys. 2011;38(4):2168-2175.
9. Boden WE, O’Rourke RA, Teo KK, et al. Optimal medical therapy with or without PCI for stable coronary disease. N Engl J Med. 2007;356(15):1503-1516.
10. Levine GN, Bates ER, Blankenship JC, et al. 2011 ACCF/AHA/SCAI guideline for percutaneous coronary intervention: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions. Circulation. 2011;124(23):2574-2609.
11. Ge JB. Current status of percutaneous coronary intervention of chronic total occlusion. J Zhejiang Univ Sci B. 2012;13(8):589-602.
12. Sachdeva R, Agrawal M, Flynn SE, Werner GS, Uretsky BF. The myocardium supplied by a chronic total occlusion is a persistently ischemic zone. Catheter Cardiovasc Interv. 2013 May 22 (Epub ahead of print).
13. Olivari Z, Rubartelli P, Piscione F, et al; TOAST-GISE Investigators. Immediate results and one-year clinical outcome after percutaneous coronary interventions in chronic total occlusions: data from a multicenter, prospective, observational study (TOAST-GISE). J Am Coll Cardiol. 2003;41(10):1672-1678.
14. Suero JA, Marso SP, Jones PG, et al. Procedural outcomes and long-term survival among patients undergoing percutaneous coronary intervention of a chronic total occlusion in native coronary arteries: a 20-year experience. J Am Coll Cardiol. 2001;38(2):409-414.
15. Yamamoto E, Natsuaki M, Morimoto T, et al; CREDO-Kyoto PCI/CABG Registry Cohort-2 Investigators. Long-term outcomes after percutaneous coronary intervention for chronic total occlusion (from the CREDO-Kyoto Registry Cohort-2). Am J Cardiol. 2013 Jun 1 (Epub ahead of print).
16. Stone GW, Reifart NJ, Moussa I, et al. Percutaneous recanalization of chronically occluded coronary arteries: a consensus document: part II. Circulation. 2005;112(16):2530-2537.

From the ¹Department of Internal Medicine, Staten Island University Hospital, New York, New York, ²University of Arkansas for Medical Sciences, Little Rock, Arkansas, and ³Wellstar Cardiology, North Fulton Hospital, Roswell, Georgia.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Sachdeva is on the speaker’s bureau for Volcano Corporation. Dr Shah and Dr Deshmukh report no conflicts of interest regarding the content herein.

Address for correspondence: Rajesh Sachdeva, MD, North Fulton Hospital, 3000 Hospital Blvd, Roswell, GA 30076. Email: rajesh.sachdeva@tenethealth.com