RADIATION AND YOUR HEALTH: WHAT YOU SHOULD KNOW

What is Radiation?
Radiation is any energy that comes from a source and travels through space.  Examples are heat and light.  The category of radiation that has made the headlines in recent years as possibly posing a health risk is called Ionizing Radiation:  high energy radiation capable of ionizing atoms (breaking atoms apart).  Examples of ionizing radiation are x-rays and gamma rays, which are used in medical imaging.

What are the sources of radiation to the general population?
Radiation is a naturally occurring phenomenon.  Common sources of radiation in nature include the sun and the soil.  Today, half of the radiation to the general population comes from this natural background; the other half comes from “man made” sources.  The overwhelming majority of these man made sources are comprised of medical uses, including imaging equipment (about half of which comes from CT scanning).

How is radiation dose measured?
The unit of measurement of “effective” radiation dose is called a Sievert; in imaging, we commonly deal in milliSieverts (one thousandth of a Sievert).  While it is a good measuring standard to compare various imaging studies and to examine population risk, it does not accurately correlate with any individual patient risk because of multiple factors discussed below.  The natural background radiation dose to the general population is about 3.5 milliSieverts per year.

What are the risks of ionizing radiation associated with imaging?
This is a very complex issue.  Let’s start with what we know for certain.  The major concern from ionizing radiation used in imaging is the risk of cancer induction (most of the other effects of radiation are seen with much higher levels of radiation which are not used in imaging).  Based on data acquired from populations with large exposures (eg, atom bomb and Chernobyl survivors), ionizing radiation at effective doses above 100 milliSieverts is associated with a statistically increased risk of cancer, which would  appear years to decades later.

That is where the certainty ends.  There is no definitive statistical evidence of increased cancer risk below exposures of 100 milliSieverts.  All imaging procedures involve doses less than 50 milliSeiverts (most are 10 or less).  This does not mean that such risk does not exist; only that we cannot definitely detect it.  The reasons that detecting such risk would be so difficult are that the expected worse case risk (based on extrapolated data from higher doses) would be very low (for example, 1 in 2000 for a 10 milliSievert exposure), and the natural occurrence of cancer in the general population is so relatively high (55% of males and 40% of females in the US will develop cancer at some point in their lives).  Further complicating matters is that the assumed risk for any individual patient is very variable based on differences in genetic makeup, sex, and age.  For example, the risk of identical doses causing cancer in a 90 year old is very different from a 9 year old, since such cancer would be expected to occur years to decades later.  Although we cannot definitively detect or accurately quantify the risk at these low doses for any individual patient, we assume that such risk exists in the interest of public safety.

Typical Radiation Doses from some Imaging Examinations
Doses from imaging examinations can vary significantly depending on variables such as the imaging modality, the protocols used (which are often dependent on why the examination is being performed), and patient factors (like size, shape, and heart rate).  However, below is a brief list of typical doses from several imaging studies that use ionizing radiation (ultrasound and MRI are not included since they do not use ionizing radiation).  Note that the doses listed for CT scans are for the most common “state-of-the-art” scanners that are currently in the marketplace; the newest scanners, such as those now installed at Radiology Associates of Ridgewood, reduce this dose significantly.  (See below – New Developments in CT Dose Reduction.)

2 view Chest X ray                                                    0.06-0.1 mSv
Mammogram                                                             0.13-0.7 mSv
Lumbar Spine Series                                                2 mSv
Head CT                                                                     2 mSv
Chest CT                                                                    6-8 mSv
Abd/Pel CT                                                               10 mSv
PET/CT (low dose CT)                                            10 mSv
Coronary CT angiogram                                          4 mSv (prospective)-20 (retrospective)
Myocardial Perfusion S/R Sestamibi                     12 mSv
Catheter Coronary angiogram (diagnostic)            5-16 mSv
Catheter  Coronary angio (interventional)               8-57 mSv

Risk versus Benefit
Our lives are filled with risk; we balance these risks against benefits, often subconsciously.  Imaging procedures should not be treated any differently.  While we assume that a very small risk from ionizing radiation associated with imaging exists in the interest of patient safety (as explained above), this must be balanced against the benefits.  That medical imaging continues to revolutionize clinical medicine is beyond doubt; examples include more effective surgical treatment, shorter hospital stays, elimination of exploratory surgery, better diagnosis and treatment of cancer, better treatment of stroke and cardiac conditions, and rapid diagnosis of life threatening vascular conditions.  The goal of imaging is to reduce uncertainty about a patient’s health; denying a patient an imaging test when such a test is indicated introduces the risk of the natural history of the patient’s disease.

The table below compares the assumed risk of fatal cancer from a CT scan with a 10 milliSievert dose (again, ignoring individual patient variables such as patient age) to some other death causing risks:


Risk graph

And here is a list of estimated lifetime risk of death per 2000 individuals from various causes:

Cancer                                                                        456
Car accident                                                               24
Radon in home (average)                                         6
Pedestrian Accident                                                  3.2
Drowning                                                                     1.8
10 milliSievert exposure (assumed risk)                 1
Bicycling                                                                      0.4
Lightning Strike                                                           0.026

It should be kept in mind that risks can be viewed in 2 alternative ways.  For example, when one states that something carries a 1 in 2000 chance of causing cancer, one can also state that it has a 99.95% chance of not causing cancer.

So what precautions does Radiology Associates of Ridgewood take and what precautions should we all be taking?
Proper use of imaging procedures is a responsibility that falls on everyone involved: the ordering physician, the patient, and the imaging facility.  Every imaging study ordered should be justified on medical grounds after weighing the potential benefits and risks.  Once the decision has been made to image, the appropriate imaging test should be requested; tests that do not use ionizing radiation should be selected if they will provide the needed information.  Finally, the imaging facility should optimize the examination to obtain the needed information with the least radiation possible.
Radiology Associates of Ridgewood has been taking precautions to reduce the dose of radiation exposure to each patient when receiving imaging tests involving radiation.  Radiology Associates of Ridgewood is a proud sponsor of the Image GentlyTM campaign that seeks to reduce radiation exposure to children and the Image WiselyTM campaign to deepen the understanding of radiation protection for adults.  We thereby pledge to:

  1. To put our patient's safety, health, and welfare first by optimizing imaging examinations to use only the radiation necessary to produce diagnostic quality images; 
  2. To convey the principles of the Image Wisely program to the imaging team in order to ensure that our facility optimizes its use of radiation when imaging patients;
  3. To communicate optimal patient imaging strategies to referring physicians, and to be available for consultation;
  4. To routinely review imaging protocols to ensure that the least radiation necessary to acquire a diagnostic quality image is used for each examination.

New Developments in CT Dose Reduction
The vendors of CT scanning equipment continue to make progress on reducing CT dose.  The most recent efforts have centered around improving the reconstruction of the x-ray data into images by modeling of system statistics and system optics.  This significantly reduces image noise, thereby allowing use of much lower levels of radiation to obtain those images.

Radiology Associates is now a completely “low dose” CT center.  Both of our scanners use variants of these “low noise” image reconstruction algorithms, thereby assuring you of a low dose examination.  One of our scanners reduces radiation dose by 20-50% compared with other state of the art scanners. The FDA has recently approved a scanner and reconstruction algorithm system called “Veo” that allows for CT dose reduction of up to 60-90%, while at the same time improving image quality.  On this scanner, some examinations can be performed with 1 mSv or less radiation dose.  Radiology Associates is pleased to announce that we have just installed one of the the first such systems in the US. 

Dose reduction of this magnitude certainly represents a sea change in the use of CT.  But it also represents a challenge to the imaging community, since scanners with these levels of dose reduction will be in the minority for some time.   It is our intention to triage patients for the two scanners whenever possible using certain guidelines.  In particular, the Veo scanner will be targeted towards:

  1. Youger patients, who are theoretically more susceptible to radiation induced injury;
  2. CT studies that typically involve higher radiation doses such as CT angiography and CT Urography;
  3. Patients with medical conditions that are expected to require multiple follow-up CT studies, such as cancer, lung nodules, urinary stone disease, and aortic aneurysms.