How do I Know Whether I’m Getting Too Many X-Rays and Too Much Radiation?

What is radiation?

Radiation is best described as energy moving through space, and it can take many forms, including visible light, x-rays, gamma-rays, microwaves, and radio waves. Radiologists use low dose radiation in the form of x-rays to create images of different parts of your body. High doses of radiation can also be used to treat certain types of cancer.

Where does radiation come from?

Radiation is all around us. The two main sources of ionizing radiation are from natural background radiation and medical exposure (CT scans and x-rays). Natural background radiation comes from the Sun (cosmic radiation), the Earth (mostly Radon gas), and from naturally radioactive substances in our body. Natural background radiation exposure accounts for an average of 3.1 mSv/yr with variations depending on where you live. The average radiation exposure to individuals in thus is 6.2 mSv/yr which includes natural background and medical imaging.

What are x-rays?

X-rays are a type of radiation used in medical imaging much like a camera uses visible light to create an image. X-rays pass through the body and create an image on film based on how many x-rays get absorbed and how many pass-throughs. These films are commonly referred toes “x-rays,” but x-rays are actually the type of radiation that is used to produce the image. Studies that use x-rays include plain films, fluoroscopy, and computed tomography (CT scans).

Understanding Risk

It is important to realize that in a properly performed individual exam, the potential health benefits almost should always outweigh the potential risks of radiation exposure. However, there is data to suggest that high doses of radiation increase your future risk of cancer. This data is compiled from high dose exposures including survivors of atomic bombs and radiation spills.

You will hear a lot about x-radiation as the cause of increased cancer mortality. Some say minimum cause some say up to 10% and more increased cancer deaths. There is no definite proof, however, that the low doses of radiation used with common x-rays or CT scans cause cancer. But we know enough and should be prudent enough  to attempt to use this technology carefully and only when needed.

Typical Radiation Doses Comparison

Exam Dose in mili-Severts as a measure of radiation (mSv).


Just being alive on earth exposes each human being to  natural background radiation of  3.1 (mSv) per year  with the average US Exposure being 6.2 mSv/ year;

Dental x-rays 0.01;

Airline Flight 0.02;

Mammogram 0.04;

Chest x-ray 0.10;

Chest CT 7.0;

Abdominal CT 8.0

Comparison Doses

Natural Background

3.1 mSv/year10

Domestic Pilots

2.2 mSv/year11

Average US Exposure

6.2 mSv/year10

7 Hour Airline Flight

0.02 mSv12

Chest x-ray (2 views)

0.10 mSv

Chest CT

7.0 mSv

Estimated Lifetime Risk of Death from Various Sources13

Motor Vehicle Accident

1% or 1 in 100 chances


0.1% or 1 in 1000 chances

Bicycle Accident

0.01% or 1 in 10,000 chances


0.001% or 1 in 100,000 chances

Keep in mind, the overall lifetime risk of developing an invasive cancer is 37.5% (1 in 3) for women and 44.9% (1 in 2) for men regardless of imaging and x-ray  history.

 These statistics are averages and do not predict what is going to happen to you. They do not take into consideration individual risk factors including lifestyle (smoking, diet, exercise, etc), family history (genetics) or radiation exposure. The majority of cancers occur later in life and the average lifetime risk of dying from cancer is 25% (1 in 4).



It is currently estimated that 62 million CT scans are obtained in the United States each year.1  While debated, a recent study suggests that radiation exposure from medical imaging may be responsible for 1-3% of cancers worldwide.2 In light of recent media coverage focusing on the increased risk of cancer from CT scans, patients and physicians have become more concerned about the increased use of medical imaging.  Patients are asking their primary care providers and emergency room physicians for information about their risk. In 2004, Lee et al. concluded that “patients are not given information about the risks, benefits and radiation dose for a CT scan”.3 Additionally, this study found that both patients and physicians were “unable to provide accurate estimates of CT doses”.3

While the need for education in this area has clearly been established, there are no widely available resources that provide information to both patients and health care providers about the increased risk of cancer from medical imaging. is an educational website that focuses on estimating this risk. One of the site’s main features is a web based
calculator that allows users to track their imaging history and estimate their personal risk, while providing answers to frequently asked questions.

There are no published studies that prove the direct causality between medical imaging and increased cancer risk. Current data on radiation exposure and cancer risk is based on data from survivors of atomic bombs, nuclear accidents and the early use of x-rays.  The assumed increased risk of cancer from low dose medical exposure (CT scans and x-rays) is based on individuals exposed to high doses (atomic bombs and nuclear accidents). The theory that the increased risk holds true at these lower doses is called the linear no threshold model, and is the currently adopted model for calculating radiation risk.

Great effort has been made throughout the medical community to ensure patient safety while providing quality diagnostic images. It is important to realize that in a properly performed individual exam, the potential health benefits almost always outweigh the potential risks of
radiation exposure. Simply put, patients should not hesitate having a study if it is medically indicated.

These sites aims to provide accurate information for patients and health care providers to facilitate well-informed discussions about the increased risk of cancer from low dose radiation exposure.




The American College of Radiology (ACR) and the International Atomic Energy Agency (IAEA) both recommend hospitals monitor radiation exposure. It may be some time before all hospitals have the ability to track individual exposure. This site allows patients to log-in, create their own imaging record and generate an X-ray Risk Report with information about cancer risk.

*From Hanley , Koonce & Brashaw of the American College of Radiology


1. Brenner DJ, Hall EJ. Computed Tomography – An Increasing Source of Radiation Exposure. NEJM 357: 2277-84, 2007.

2. Berrington de Gonzalez A, Darby S. Risk of cancer from diagnostic x-rays: estimates for the UK and 14 other countries. Lancet 2004; 363:345-51.

3. Lee CI, Haims AH, Monico EP, et al. Diagnostic CT Scans: Assessment of Patient, Physician, and Radiologist Awareness of Radiation Dose and Possible Risks. Radiology 231 (2): 393-398. (2004).

4. National Research Council. Health risks from exposure to low levels of ionizing radiation. BEIR VII Phase 2. Washington, DC: National Academies Press; 2006.

5. Mettler FA, Huda W, Yoshizumi TT, Mahesh M: "Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog." Radiology 2008 248: 254-263.

6. American Cancer Society: Cancer Facts and Figures 2008.

7. Office of Communications and Public Liaison and the Radiation Safety Branch of the Office of the Director, National Institutes of Health. Fact Sheet: What We Know About Radiation.

8. Huda W, Ogden KM, Khorasani MR: Converting Dose-Length Product to Effective Dose at CT. Radiology 248:995-1003, 2008.

9. Brody AS, Frush DP, Huda W, et al: Radiation Risk to Children From Computed Tomography. Pediatrics, 120 (3): 677-682, 2007

10. NCRP Report No. 160, Ionizing Radiation Exposure of the Population of the United States. Available at Accessed April 2009.

11. Health Physics Society: Radiation Exposure During Commercial Airline Flights. Available at Accessed September 2009.

12. Mnyusiwalla A, Aviv RI, Symons SP: Radiation dose from multidector row CT imaging for acute stroke. Neuroradiology 51:635-640, 2009.

13. McCollough CH, Guimaraes L, Fletcher JG: In Defense of Body CT. AJR 193:28-39, 2009.

14. ACR Statement on Airport Full-body Scanners and Radiation, January 2010.

15. Balon HR, Roff E, Freitas JE, et al: Society of Nuclear Medicine Procedure Guideline for C-14 Urea Breath Test. Version 3.0, June 23, 2001

16. Calicchia A, Chiacchiararelli L, DeFelice C, et al: Assessment of radiation dose to patients in hysterosalpingography. Radiol Med 95(1-2): 93-7, 1998.

17. Platts D, Brown M, Javorsky G, et al: Comparison of fluoroscopic versus real-time three-dimensional transthoracic echocardiographic guidance of endomyocardial biopsies. Eur J of Echocardiography 11, 637-643, 2010.

18. Hendrick ER: Radiation Doses and Cancer Risks from Breast Imaging. Radiology, 257 (1), 246- 253, 2010."



• Don’t get any study you don’t need.

• Ask your physician whether & how the benefits of study outweigh potential risks.

• Keep a history of your studies in a diary form by date and type to avoid unnecessary repeat exams and so that the new exam can be compared to the previous exam.


For  help along these lines use these  two very valuable sources of information. ; 

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