Images are obtained with patients lying down on a table which moves through a rotating x-ray tube. Multiple sequential images are obtained using x-rays that are reconstructed in slices to provide detail of internal organs. The tube can look much like a MRI scanner, but MRI's usually take between 30 minutes to an hour, while CT scans only take a few seconds.
Radiation is simply energy moving through space. Radiation can take many forms, including visible light, x-rays, gamma-rays, microwaves, radiowaves, etc. This site specifically addresses high energy or ionizing radiation, which includes x-rays obtained in a medical imaging center. Ionizing radiation has many uses, e.g., sterilization of food and medical equipment, creation of medical images, and even in the treatment of certain types of cancer.
Because there is no scientifically proven link between cancer and low dose radiation exposure from medical imaging, there are many theories which try to estimate the risk. One such model or theory is the Linear No Threshold Model in which suggests a linear relationship exists between exposure and increased risk of cancer. This model assumes that even the smallest amount of radiation results in the smallest fraction of increased risk. Opposing theories suggest there is a level of radiation below which there is no increased risk of cancer. Currently, the most widely accepted model is the Linear No Threshold Model to ensure the highest standard of patient safety.
X-rays are a type of radiation that are created using large amounts of electricity in a x-ray tube. X-rays are 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 through. The film is commonly referred to as an "x-ray", but x-rays are actually the type of radiation used to make the image. Studies that use x-rays include plain films, fluoroscopy and computed tomography (CT scans).



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. This site 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.

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A committee of scientists and educators gathered by the National Research Council and organized by the National Academy of Sciences published their report on the Health Risks From Exposure to Low Levels of Ionizing Radiation in 2006. Table 1 was adapted from their Biological Effects of Ionizing Radiation (BEIR) VII Phase 2 Report. 4 The table estimates the number of additional cases of cancer attributable to a single dose of 0.1Gy (100 mSv) for different age groups. Data is based on the incidence of all cancer types. Data was plotted (Graph 1), exponential curves were drawn through the data points and formulas derived. Table 2 was adapted from Mettler et al and lists average adult doses for various medical imaging studies 5. The conversion factor used for the Brain and Neck CTA/CTP is 0.00345 12. The conversion factors used to Convert Your Dose from Dose Length Product (mGy · cm) to Effective Dose (mSv) were 0.0022 mSv/mGy · cm for Head CT, 0.0054 mSv/mGy · cm for Neck CT and 0.0180 mSv/mGy · cm for Body CT. 8 The Risk Calculator can also be used to convert Dose Length Product (DLP in mGy · cm) to Effective Dose (ED in mSv).

Click the images for an enlarged view

Table 1
Graph 1
Table 2


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The content of this website has been reviewed by our medical team.

Mike Hanley, MD

Mike Hanley, MD
Founder and Editor



Jay Koonce, MD
Contributing Editor



Marques Bradshaw, MD
Contributing Editor


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Image Wisely - Radiation Safety in Adult Medical Imaging (

Image Gently - The Alliance for Radiation Safety in Pediatric Imaging (

Nuffield Health - Educational Radiation Video (

Health Physics Society - Specialists in Radiation Protection ( - Radiology information resource for patients (


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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. 2008CAFFfinalsecured.pdf Cancer Incidence)

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. Available at Accessed December 16, 2008

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." (

19. Heusch P, Kropil P, Buchbender C, et al: Radiation exposure of the radiologist’s eye lens during CT-guided interventions. Acta Radiologica 2014, Vol 55(1) 86-90. (

20. Richards PJ, George J, Metelko M, et al: Spine computed tomography doses and cancer induction: Spine 35(4), 430-433 2010. (


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Together, dedicated to improving the understanding of radiation risks from medical imaging. Calculate your dose and estimate cancer risk from studies including CT scans, x-rays, nuclear scans and interventional procedures.