Radiation Dose in MS - CT coronarography

Radiation DoseRadiation Dose in in MSMS--CT coronarographyCT coronarography

Ladislav Pavic, MD, PhDLadislav Pavic, MD, PhD

Sunce Clinics Zagreb / SarajevoSunce Clinics Zagreb / Sarajevo

Croatia / Bosnia & HerzegovinaCroatia / Bosnia & Herzegovina

With 64 ≥ slice CT scaners, CCTA has emerged as a useful diagnostic imaging modality for the assessment of coronary artery disease.

It is considered appropriate for selected indications:patients with a low-to-intermediate pretest probability for obstructive CADrapid evaluation of patients with chest pain in emergencyby-pass analysisetc.

The clinical usefulness of CCTA has to be weighed against the radiation exposure and the small but potential risk of cancer induction!

ACCF/ACR/SCCT/SCMR/ASNC/NASCI/SCAI/SIR 2006 appropriateness criteria for cardiac computed tomography and cardiac magnetic resonance imaging: a report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American College of Radiology, Society of Cardiovascular Computed Tomography, Society for Cardiovascular Magnetic Resonance, American Society of Nuclear Cardiology, North American Society for Cardiac Imaging, Society for Cardiovascular Angiography and Interventions, and Society of Interventional Radiology. Hendel RC, et al. J Am Coll Cardiol. 2006;48:1475-1497.

Introduction

Introduction

Computed tomography represents an important source of ionizing radiation arising from medical exposures

Since the inception of CT in the 1970s, its use has increased rapidly. It is estimated that more than 62 million CT scans per year are currently obtained in the US

Small series reported CCTA radiation doses of up to 21.4 mSv without use of electrocardiographically controlled tube current modulation

Other small series reported radiation doses as low as 2.1 mSv with the application of newly available sequential scanning algorithms.

Although the risks for any one person are not large, the increasing exposure to radiation in the population may be a public health issue in the future.

Gerber TC, et al. Ionizing radiation in cardiac imaging: a science advisory from the American Heart Association Committee on Cardiac Imaging of the Council on Clinical Cardiology and Committee on Cardiovascular Imaging and Intervention of the Council on Cardiovascular Radiology and Intervention. Circulation. 2009 Feb 24;119(7):1056-65. Epub 2009 Feb 2.

Measuring radiation - Dosimetry

Effective dose (E, SI units - mSv):

reflects the risk of the biological effects of ionizing radiation,

represents the amount of whole-body irradiation that would yield a biological risk equivalent to that of an irradiation to only a portion of the body,

such as that which occurs during a diagnostic or therapeutic medical procedure,

is useful in comparisons of the biological risk of different medical procedures that use ionizing radiation,

given the uncertainties regarding organ risk and the inability of E to reflect individual patient risk, differences between estimates of the E by a factor of less than 2 cannot be considered significant


Risks related to exposure to ionizing radiation

The hypothetical complication of diagnostic radiation exposure that is of greatest concern, the risk of inducing malignancies, is a stochastic or random effect…

No threshold below which radiation cannot cause malignancies and that the risk of malignancies increases linearly with radiation dose.

Age- & gender averaged lifetime risk of dying of a malignancy attributable to radiation exposure was estimated to be 5-7.9% of the general population per 1 Sv of E

In individuals receiving an estimated E < 100 mSv, the relative risk of developing solid tumors was not statistically significantly different from no increased risk


National Council on Radiation Protection and Measurements (NCRP). Risk Estimates for Radiation Protection. Bethesda, Md: National Council on Radiation Protection and Measurements; 1993. Report No. 115.

Risk associated with activities in daily life

All people are exposed to background radiation due to cosmic rays, radon, and other low-level radiation sources that on average amount to ≈ 3 mSv per year (range, 1 to 10 mSv)

This makes it difficult to discern between the risk attributable to a single exposure to medical radiation and the risk of the exposure to natural background radiation

The population-averaged lifetime risk of developing a malignancy in the United States is 41%, and the risk of dying of a malignancy is 21%

The estimated increase in the lifetime risk of dying of a malignancy associated with 10 mSv (typical CCTA) of ionizing radiation is ≈ 0.05%

The relative risk of lung cancer ranged from 4.9 in individuals who smoked 1 to 15 cigarettes per day to 13.3 in individuals who smoked >25 cigarettes per day.

The relative risk of lung cancer associated with an E of 1000 mSv (app. 50 to 100 CCTAs) was 2.2.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). Epidemiological studies of radiation and cancer. Paper presented at: 54th Session of UNSCEAR; May 29–June 2, 2006; Vienna, Austria.

Ries LAG, et al. SEER Cancer Statistics Review, 1975–2004. Bethesda, Md: National Cancer Institute; based on November 2006 SEER data submission, posted to the SEER Web site, 2007. Tables I-14 and I-17: Lifetime risk (percent) of being diagnosed with cancer and lifetime risk (percent) of dying from cancer, by site and race/ethnicity. Available at http://seer.cancer.gov/csr/1975_2005/results_merged/topic_lifetime_risk.pdf. Accessed January 1, 2009.

Pierce DA, et al. Joint effects of radiation and smoking on lung cancer risk among atomic bomb survivors. Radiat Res. 2003; 159:511–520.

Recommendations by AHA Science Advisory Committee on Cardiac Imaging

Imaging studies that expose patients to ionizing radiation should be ordered only after thoughtful consideration of the potential benefit to the patient and in keeping with established appropriateness criteria

Considerations should include options for answering the clinical question at hand by means that do not use ionizing radiation or choosing the type of study that exposes the patient to the lowest amount of radiation.

Routine surveillance radionuclide stress tests or CCTA in asymptomatic patients at low risk for ischemic heart disease are not recommended

because there are no prospective, randomized trials that demonstrate that CCTA can convey survival benefit

Once it has been established that CCTA is needed, every effort should be made to reduce patient dose while balancing image noise and quality sufficient for confident interpretation


CCTA, Images, example

Contact: [email protected]

Radiation Dose in MS - CT coronarography

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