A 101 on
Medical
Radiation
Exposure
INTRO • 101 QUICK-GUIDE
UNITS • SIEVERTS • mSv • REMS • mrem • CONVERSIONS
NATURALLY-OCCURRING "BACKGROUND" RADIATION EXPOSURE
CATEGORIES OF EXPOSURE
ALL- SOURCE COMPARATIVERADIATION EXPOSURE
WHOLE-BODY BACKSCATTER SCANNERS
RADIATION RISKS WITH DENTAL RADIOGRAPHY
UNDERESTIMATION OF CT SCAN RADIATION / RISKS
HOW MUCH IS TOO MUCH?
WHAT PATIENTS SHOULD DO

INTRO
• The page is meant to be a quick guide for radiation exposure related to various medical procedures. As a basis for comparison of radiation exposure associated with medical procedures, the annual 3 mSv of naturally-occurring background radiation exposure is used as a baseline value. Another comparative table for all-source exposures uses the same 3 mSv of background radiation as starting point and the tsunami numbers of nuclear reactor meltdowns as high-end values of exposures.
• The source articles used for this info-page provide differing values in the millisieverts of exposure associated with some radiologic procedures. Some differences may be partly explained by duration of exposure and type of equipment in use. Also, the estimation of radiation dosage is an inexact science, and the numbers should be considered as best approximations.


UNITS • SIEVERTS • mSv • REMS • mrem • CONVERSIONS
• mSv / millisievert / mSievert: A scientific unit of measurement for radiation dose, referred to as effective dose, is the mSv or millisievert. There are other radiation dose measurements: rad, rem, Roentgen, Sievert, and Gray. However, most articles and reports utilize the millisievert - mSv.
• Sievert (Sv) - the unit measures the equivalent dose of radiation (H), supposed to have a damaging effect equivalent to the same dose of gamma rays.
• Gray (Gy) - measures the absorbed dose of radiation (D), absorbed by any material.
• SI - both the gray (Gy) and the sievert (Sv) are SI derived units, defined as a unit of energy (joule) per unit of mass (kilogram).
• In the United States, the rem still often used.
• The conventional unit for its time derivative is mSv/h.

• Conversions
          1 rem = 0.01 Sv = 10 mSv
          1 mrem (millirem) = 0.01 mSv = 10 μSv
          1 Sv (sievert) = 100 rem
          1 mSv (millisievert) = 100 mrem = 0.1 rem
          1 mSv = 0.001 Sv
          1 μSv (microsievert) = 0.1 mrem
          1 μSv = 0.000001 Sv

NATURALLY-OCCURRING "BACKGROUND" RADIATION EXPOSURE
• There are natural sources of radiation to which we are exposed to all the time; in the U.S. the estimated effective dose is about 3 mSv per year, or 300 mrem/year. (Some reports use 3.6 mSv are the annual background exposure.)
• Naturally occurring radioactive materials can be from cosmic radiation high up from outer space. A coast-to-coast round-trip flight in a commercial airplane adds about 0.03 mSv of cosmic rays. At ground level, a major contributor is the radon gas from our homes, as much as 2 mSv per year.
• As a basic comparison, a chest x-ray is equivalent to 10 days of naturally-occurring background radiation. (See table below)

ALL-SOURCE COMPARATIVE EXPOSURES IN MILLISIEVERTS (mSv)
Naturally-occurring annual background radiation 3
Round-trip coast-to-coast commercial air travel 0.03
Airport backscatter scanner 0.05
Chest X-ray (2 views) 0.1
Mammography 0.4
Annual Exposure of Airline crew flying a NY-Tokyo polar route 9
CT chest 7
CT scan: full-body 10
CT scan: abdomen and pelvis 15
CT scan: heart 16
Maximum allowable exposure for U.S. radiation workers 50 / yr
Radiation dose at boundary of Fukushima Daiichi on March 16, 2001 1.9 / hr
Recommended limit for radiation workers every five years 100
Lowest annual dose at which any increase in cancer is evident 100
Level for relocating people after Chernobyl accident 350 / Lifetime
Peak radiation recorded at Fukushima Daiichi nuclear site, 15 March 2011 400 /hr
Accumulated dosage to cause fatal cancer many years later in 5% of people 1,000
Single non-fatal dose that will cause radiation sickness 1,000
Single dose that would kill half of those exposed to it within a month 5,000
Typical exposure to Chernobyl workers who died within a month 6,000
Single dose, fatal within a few weeks 10,000

CATEGORIES OF EXPOSURE
Low under 3 mSv per year. About what one accumulates yearly from background radiation in the US without undergoing imaging procedures.
Moderate Up to 20 mSv per year. This is the 5-year annual average of those working with radiation equipment.
High up to 50 mSv per year. This is the annual limit for people working with radiation equipment.
Very high more than 50 mSv per year.

BEIR (Biologic Effects of Ionizing Radiation)
• X-rays and gamma rays are sources of low linear energy transfer (low-LET) ionizing radiation. Humans are exposed to ionizing radiation from both natural and man-made sources.
• Most radiation sources are a mixture of high- and low LET radiation. Low-LET radiation deposits less energy in the cell along the radiation path and is considered less destructive per radiation track. BEIR defines low LET radiation as a dose between near zero to about 100 mSv (0.1 Sv). As points of comparison, annual background radiation in the U.S. is 3 mSv; a CXR exposure, about 0.1 mSv; and a whole body CT, about 10 mSv.
• Worldwide background radiation of 2.4 mSv / year comes from:
  High-LET: inhalation exposure to radon 52 %
  High-LET: ingestion 5 %
  High-LET: neutron component of cosmic radiation 4 %
  Low-LET: directly ionizing and photon component of cosmic radiation 12 %
  Low-LET: radiation exposure from the earth 20%
  Low-LET: ingestion 7 %
• In the US population, 79% of man-made radiation exposure is from medical xrays and nuclear medicine; consumer products (tobacco, domestic water supply, building materials, and to a lesser extent, smoke detectors, TV, computer screens contribute about 16%; occupation exposures, fallout, and nuclear fuel cycle contribute about 5%.

COMPARATIVE RADIOLOGIC MEDICAL EXPOSURES
X-rays are forms of radiant energy, like light or radio waves; but unlike light, they can penetrate the body to allow the visualization of internal structures through film or monitors: plain xrays, fluoroscopies, CT scans, mammography, etc.
Source
Effective Radiation
Dose
 Compared to Natural Background Exposure
of 3 mSv/year
Natural background exposure 3 mSv / year  
Airport Backscatter (Single scan) 0.05 mSv 30 mins
Coast-to-coast round trip
     commercial flight		 about 0.03 mSV
of cosmic rays		 18 mins
Head and Neck
CT - Head 2 mSv 8 months
CT - sinuses 0.6 mSv 2 months
Dental radiography * 0.07 mGy / 4 bitewings 0.02 mGy / panoramic 0.24 mGy / full-mouth exam
Chest / Heart / Lungs
CXR (chest x-ray, 2 views) 0.1 mSv 10 days
CT - chest 7 mSv 2 years
CT - chest / low-dose 1.5 mSv 10 days
Cardiac CT / Calcium Scoring 2 mSv 2 months
Coronary CT angiography 8 - 20 mSv 3 - 7 years
Coronary angiography 5 mSv < 2 years
Coronary MSCT 10 mSv > 3 years
Resting scan plus
Technetium-99 sestamibi
      cardiac stress scan		 11.3 msv < 4 years
Dipyridamole nuclear stress test (Thallium + technitium) 25 msv > 8 years
Abdomen
Upper GI series 5-6 mSv 1.5 - 2 years
Lower GI series (Barium Enema) 7 - 8 mSv 3 years
Abdomen x-ray (AP) 0.7 mSv 3 months
KUB x-ray (2 views) 1.2 mSv 4 months
CT Abdomen 8 mSv 2 1/2 - 3 years
CT Abdomen / Pelvis (combined) 10 - 15 mSv 3 - 5 years
CT, Body 2 - 10 mSv  
CT / Colonography 10 mSv 3 years
IVP (Intravenous pyelography) 3 mSv 1 year
Ureteric stent insertion 4.7 mSv 20 months
Voiding Cystourethrogram 1.6 mSv (5-10 years old)
0.8 mSv (infant)		 6 months
3 months
Skeletal    
Spine x-ray 1.5 mSv 6 months
Extremity x-ray 0.001 mSv Less than 1 day
CT - Spine 6 mSv 2 years
Myelography 4 mSv 16 months
DEXA (Bone densitometry)
           Male or Female		 0.001 mSv Less than 1 day
Women's Imaging    
Galactography 0.7 mSv 3 months
Hysterosalpingography 1 mSv 4 months
Mammography 0.4 - 0.5 mSv 2 months
Others    
CT - Whole Body 2 - 10 mSv 6 months to 3 years
 
Note: Some use 3.6 mSv as the amount of naturally-occurring background radiation exposure.
Note:The estimation of radiation dosage is an inexact science, so these numbers listed should be considered as best approximations.
Note: Radiation exposures vary depending upon the equipment and patient.

WHOLE-BODY BACKSCATTER SCANNERS

Whole-body backscatter scanners are being deployed in airports across the United States. The scanner delivers narrow, low-density, high-speed xray beams over the entire person, front-and-back, to detect any hidden weapons or explosive devices. The dose from a backscatter scan may be as low as 0.05 uSv (equivalent to about 30 minutes of natural background radiation, or 4 to 5 minutes of air travel, or lee radiation exposure than one gets from eating a banana). Also, at a dose of 0.05 to 0.10 uSv, the 250 limit would be reach only if a person is scanned 2,500 to 5,000 times per year; highly improbable for any traveler. (Medscape)

Millimeter Wave Machines: Another concern with backscatter scanners are privacy issues. The scanners provide very detailed body images, some calling them R-rated. Because backscanner machines could not meet the deadline on Congress mandated software to make the images more generic and less embarassing, backscatter scanners have beomce history in airports, to be replaced by millimeter wave machines by June 2013. Millimeter wave models use radio waves, so there is no ionizing radiation. (Sandra Fryhofer / Medicine Matters / September 2013 / Medscape)

RADIATION RISK FROM DENTAL RADIOGRAPHY
Radiation from dental radiography is so low it is highly unlikely to cause measurable risk. Brain exposure from 4 bitewings is about 0.07 mGuy, about 0.02 mGy for a panoramic exam, and 0.24 mGy for a full-mouth exam consisting of 12 periapical and 4 bitewing exposures. (A bitewing is a dental film for simultaneous xraying the crowns of the upper and lower teeth, help in place by a tab between the teeth.) In comparison, brain exposure from head CT is in the range of 43-75 mGy. A report concurs with the Claus study that suggests an association between dental radiography and meningiomas, but it is more likely the hemangiomas trigger the need for dental imaging than the other way around. (Medscape)

UNDERESTIMATION OF CT SCAN RADIATION / RISKS
• Study participants had poor understanding of the risks associated with CT scanning. The majority underestimated the XR radiation from CT scans and cancer risk comprehension was poor.
• Many were unaware that 2 or 3 abdominal CT scans exposed a person to the same amount of radiation exposure as experienced by Hiroshima survivors who lived near the atomic blast.
• The radiation dosage from one scan typically ranges from a few mSv (comparable to a year's worth of background radiation) to ten of mSv.
• A CT scan that delivers 5 mSv of radiation is equivalent to 50 chest x-rays. A four-phase abdominal CT gives the same radiation as 300 chest x-rays.
• Hiroshima survivors living a few miles from the blast received between 5 to 100 mSv. There is little difference between beamed hospital procedure radiation and mix of x-rays and gamma radiation from a nuclear explosion. A difference is that atomic bomb survivors got whole-body radiation compared to the direct CT radiation exposure.
• In the U.S. the use of CT scans has skyrocketed in the past 3 decades, from 3 million scans in the 80s to 70 million scans in 2007. More than 4-7 million children are getting CT scans, a number that increases by 10% a year. The increase radiation exposure estimates 29,000 new cases of cancers in the coming years.
• A retrospective cross-sectional study describing radiation dose associated with 11 of the most common types of diagnostic CT procedures concludes: Radiation doses from the commonly performed diagnostic CT examinations are higher and more variable than generally quoted.

HOW MUCH IS TOO MUCH?
• Experts, scientists, and radiologists agree radiation in large doses causes cancer. The controversy and debate centers on what is the "acceptable" dose.
• Some experts espouse the linear-no-threshold (LNT) theory for radiation cancer risk - that any radiation dose, no matter how small, can cause cancer, i.e., the risk is never zero.
• Some experts disagree, stating cancer risk with low exposure is overstated. Using rem unit, no risk of adverse health conditions has been established for exposures to 5,000 millirem (marram) or less.
• The Health Physics Society recommends against quantitative estimation of health risk for individual exposures of 5,000 marram (millirem) . The threshold of radiation above which cancer risks begins to increase is proposed to be about 10,000 marram.
• A radiation dose of 50 mSv starts concerns regarding human health: 100 mSv and above raise the risk for developing solid cancers and leukemia.
• Recent estimates suggest 2% of cancers could be attributed to CT scan radiation. Although single exposures may be minimal, cumulative exposures increase the risk.

WHAT PATIENTS SHOULD DO
• Keep a record of your radiation exposure history: X-rays, CT scans, nuclear imaging, barium studies; especially if you're changing physicians or seeing different doctors, specialists, and consultants.
• Avoid repetitive tests.
• Most doctors are not aware of the cumulative dose of radiation their patients have received.
• Although it is your doctor's responsibility to weight the benefits of imaging against risks, be interactive in the decision making needed with your work-up. Try to be informed. Discuss alternative workup procedures that deliver less radiation: limited scanning, ultrasounds, MRI. Some doctors are just too busy or more concerned with the caking aspects of their practice; some might have vested interests on procedures and scanners. If so, look for another doctor. And, second opinions won't hurt.
• Go to facilities committed to radiation safety. Check out the age of the facility's equipment. Old CT scanners deliver a lot more radiation than the newer ones. Radiation dosages differ significantly between sites/centers and CT systems.
• Search out facilities using new software technology that can significantly reduced the required radiation dose.
• A study using dose-reduction strategy, performed a 64-slice CT angiogram with a measured radiation exposure of 2.1 mSv. In comparison, other centers performed similar CT angiogram using 21 mSv, 10 times the level of radiation.
• Newer scanners - Electron Beam CR , multi detector computed tomography (MDCT), low-dose hi-def CT scanners, are in use or in research-and-development, delivering only a fraction of radiation while achieving high image quality.


Sources and Suggested Readings
Are Full-Body Airport Scanners Safe? / Medscape

Cancer Risk Overestimated With Radiation From CT Scans / Medscape Medical News
Patient Perceptions of Computed Tomographic Imaging and Their Understanding of Radiation Risk and Exposure / Ann of Em erg Me / Abstract
Radiation Exposure Tied to Lymphoma Risk in Men / Am J Epidemics 2009;169:969-976 / ACR
Radiation Dosage of EBT Procedures / prepared by Dr. Alan Boyer
Radiation Dose in Computed Tomography of the Heart: Morin RL,  Gerber TC, MD & McCollough CH; Circulation 2003;107:917-922.
Reduced Radiation Exposure with the Use of an Air Retrograde Pyelogram During Fluoroscopic Access for Percutaneous Nephrolithotomy / Lipkin ME, Mancini JG, Ziberman DE et al / Journal of Endourology (Mar 2011)
Radiation Protection in Urology /
Radiation During Cardiovascular Imaging / Ariel Roguin and Prashant Nair / From British Journal of Cardiology / Medscape
Radiation Dose Associated With Common Computed Tomography Examinations and the Associated
Lifetime Attributable Risk of Cancer / Rebecca Smith-Bindman, MD; Jafi Lipson, MD, Ralph Marcus, BA, Kwang-Pyo Kim, PhD et al / Arch Intern Med. 2009;169(22):2078-2086
Radiation exposure: a quick guide to what each level means / DataBlog
Sievert / Wikipedia
CT Scans of the Heart Can Be Done with Low Radiation Dose /New Study Shows Wide Variation in Centers; Calls for Increased Education and Training to Achieve Optimum Results / Angioplasty.Org/Imaging News
Ultra-Low Radiation Dose Renal CT Examinations / Janet Cochrane Miller, D Phil., Author / Radiology Rounds, June 2011, Vol 9, Issue 6
Long-Term Cancer Risks From Cardiac Imaging Radiation Remain Unknown / Marlene Busko / Medscape Internal Medicine News /
Beir VII: Health Risks from Exposure to Low Levels of Ionizing Radiation / Report in Brief / Expert Consensus Report
Multiple CT Scans Add Minimal Additional Cancer Risk / Daniel M. Keller, PhD / Medscape Internal Medicine News
What Are the Risks of Dental X-rays?: Radiation Risk From Dental Radiography / Sotirios Tetradis, DDS, PhD; Stuart C. White, DDS, PhD / Medscape Internal Medicine / Medscape Dentistry & Oral Health © 2012
Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging / FDA • US Food and Drug Administration
Cancer Risks Associated With External Radiation From Diagnostic Imaging Procedures / Martha S. Linet, MD, MPH; Thomas L. Slovis, MD; Donald L. Miller, MD, FSIR; Ruth Kleinerman, MPH; Choonsik Lee, PhD; Preetha Rajaraman, PhD; Amy Berrington de Gonzalez, DPhil / CA CANCER J CLIN 2012;62:75–100

Compilation of Info by Dr. Godofredo Stuart
Last Update January 2014
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