Radiation Safety

We understand that patients may be concerned about radiation exposure, and we are too.  We are a global leader in adopting practices for the reduction of radiation in all our patients. Learn about what we do to ensure your safety during imaging.

Benefits of Medical Imaging

Medical imaging, including computed tomography (CT) and X-rays, allows doctors to see inside the body, to identify and diagnose diseases, plan treatment, and manage emergencies, like a stroke. Much has recently been written about radiation, so it is important to understand imaging performed using radiation—CT and X-ray scans—and the benefits to the patient along with the associated risks. Keep in mind that radiation doses used in CT and X-ray scans are much lower than those used in radiation oncology, which uses radiation as a therapy to treat cancer. Radiology (imaging) and radiotherapy (cancer treatment) are quite different.

Most people in the United States have benefited by imaging, whether from a simple chest X-ray for a cough, a bone X-ray for a fracture, or something more complex like a CT scan. The discovery of X-rays in 1895 by Wilhelm Roentgen led to the first Nobel Prize in Physics. CT ranks as one of the top five medical developments in the last 40 years. It has proven so valuable as a medical diagnostic tool that the 1979 Nobel Prize in Medicine was awarded to the inventors of CT.

Benefits of CT imaging

• Determining when surgeries are necessary
• Reducing the need for exploratory surgeries
• Improving cancer diagnosis and treatment
• Reducing the length of hospitalizations
• Guiding treatment of common conditions such as injury, cardiac disease, and stroke
• Improving patient placement into appropriate areas of care, such as an intensive care unit

Understanding Radiation

Radiation is a form of energy (like X-rays) that travels through matter and is used to create pictures of internal body structures. It's all around us, coming from both natural and man-made sources. We are all exposed to radiation every day, mainly from the sun and soil. Other sources of radiation are man-made and include consumer products as well as diagnostic imaging tests like X-rays, CT scans, and nuclear medicine studies.

X-rays are a form of “ionizing radiation” which has enough energy to penetrate the body, which enables X-rays to produce pictures or images of internal body structures. X-rays are also used to assist with interventional procedures and to target and destroy abnormal cells during radiation therapy.

Measuring Radiation Dosage

The scientific unit of measurement for radiation dose is the Gray (Gy), which is a measure of the amount of X-ray energy absorbed per unit mass. Other radiation units include rad, rem, roentgen, and Sievert.

X-ray imaging procedures normally focus on a specific body part (for example the head or chest) and expose only that region of the body to a radiation dose. Furthermore, different tissues and organs have varying sensitivity to radiation exposure, so the actual radiation risk from an X-ray procedure will vary depending on the body part imaged and the tissues exposed. The term “effective dose” is used to account for the portion of the body exposed during a procedure, the relative sensitivities of the different tissues exposed, and averages the risk of radiation over the entire body.  More importantly, it allows for comparison to more familiar sources of exposure like natural background radiation. The unit of effective dose is the Sievert.  X-ray procedures result in a small fraction of a Sievert, usually one one-thousandth of a Sievert, indicated by a milliSievert (mSv).

CT Scans & Radiation Risk

A CT (computed tomography) scan is a special kind of X-ray examination that takes detailed pictures of the inside of your body. Doctors use these images to find out what’s wrong, treat problems, and see how treatments are working.

You might have seen news stories saying that CT scans could raise your risk of cancer. While it’s true that CT scans use radiation, these articles don’t always tell the full story and can cause unnecessary worry.

If your doctor recommends a CT scan, it’s because it can help find or treat something serious. The chance of harm from the scan is very small, and doctors work hard to keep it that way.

Talk to your doctor if you’re worried. But remember, not getting a needed scan can be riskier than having one.

This guide will help you understand the real benefits of CT scans, the small possible risks, and how doctors work to keep you safe.

Why CT Scans Are Important

• Find Problems Early – Like cancer, when it’s easiest to treat
• Handle Emergencies – Like strokes, internal bleeding, or appendicitis
• Plan Cancer Treatment – By showing where the cancer is and how it’s reacting to treatment
• Avoid Surgery – Sometimes a CT scan means surgery isn’t needed
• Guide Treatments – Like helping doctors place needles or tubes in the right spot
• Get Faster Answers – So you can start treatment sooner

Are CT Scans Dangerous?

CT scans do use a small amount of radiation. A recent study tried to estimate how this might affect cancer risk in the future, but it used math models based on data predominantly from a different population exposed to a different type of radiation — not real cases of cancer.

Here are some important facts:

• There has never been a proven case of someone getting cancer from a CT scan.
• Studies estimating cancer risk from CT radiation often use models based on data from different radiation exposures (like atomic bomb survivors).
• The way these studies estimate CT radiation may not match how CT scans work today, since modern machines use much less radiation.

Radiation Risk in Perspective

Medical procedures and tests have both risks and benefits. We need to weigh these carefully. News stories often talk about radiation dangers (risks), but these tests also help patients in important ways (benefits).

Another way to think about risk is to focus on what probably won't happen. For example, if there's a one in 2,000 chance of getting cancer from a procedure, that means you have a 99.95% chance of not getting cancer.

If you need a CT scan

• The benefit of finding or treating a serious health problem is much greater than the tiny, possible risk of cancer.
• Not getting a scan when you need one can be far more dangerous than the small possible risks of CT radiation.
• CT scans today use the lowest radiation dose possible to get clear images.

Risk-of-Death-from-Common-Occurrences-Graph.jpg

The graph shows how the potential risk of developing cancer from exposure to the dose of radiation in a typical adult CT scan of the body compares to other similar risks. For example, even if you've never smoked, you're more than twice as likely to die from lung cancer naturally than from cancer caused by a CT scan.

Our Commitment to Your Safety

Radiologists are doctors who specialize in reading a patient’s images. Here’s what we do to keep you safe:

• We follow the principle of ALARA (As Low As Reasonably Achievable). This means we use the lowest radiation dose that still provides a clear, diagnostic image.
• Keep improving scan settings to use less radiation
• Follow strict rules about when scans should be done
• Work with your doctor to choose the best type of scan for your situation
• Recommend other tests (like MRI or ultrasound) when they can be used instead

We’re very concerned about radiation—after all, we work around it every day. We’re fully committed to minimizing exposure of our patients and staff to radiation. We follow the principle of "ALARA" (radiation dose As Low As Reasonably Achievable) when it comes to radiation and patient safety. That means we always use the lowest radiation dose consistent with getting imaging results that are of appropriate diagnostic quality.

Low-Dose Protocols 

We use CT settings (protocols) that adjust the dose of radiation depending on the patient age and size, the body part being imaged, and the reason for the study. These protocols are routinely reviewed for each body part. Specific protocols are used for pediatric imaging, which minimize dose. In addition, radiation levels for CT and Interventional Radiology procedures are monitored.

Strategies to Ensure Imaging Safety

We’re fully committed to minimizing exposure to radiation for our patients and staff. Here are things we routinely do to ensure imaging is safe:

Choosing the most appropriate imaging study

Minimizing the exposure to radiation dose begins with the proper selection of an imaging study for the specific needs of every individual patient. Our radiologists work closely with and encourage referring physicians to consider tests that do not involve ionizing radiation (e.g., ultrasound or MRI) if these can provide the same information as a CT scan or other tests with ionizing radiation.

Latest CT technology for automatic radiation dose reduction

UCSF continually invests in dose reduction technology as it becomes available. Examples include the latest generation of automated dose modulation and CT image reconstruction software.

Optimizing exposure, “tube-on” time, and collimation

Dose reduction is achieved by reducing “tube-on” time and the amount of the body exposed to radiation. The “tube-on” time refers to the duration the X-ray tube is turned on and is often automatically modified during X-ray and CT exams and may be manually modified by the operator during X-ray, fluoroscopy, and interventional radiology procedures. Collimation is routinely used to carefully restrict the X-ray beam to the area of clinical interest.

Special attention to pediatric patients

Our team of dedicated pediatric radiologists works closely with pediatricians and pediatric subspecialists to minimize the use of ionizing radiation used to image children and infants, often recommending ultrasound (which does not use radiation) when indicated. When imaging using ionizing radiation becomes necessary, state-of-the-art radiation reduction techniques and low dose protocols (for CT) are employed.

Careful quality control

Quality control procedures are routinely performed to further minimize the potential risks of radiation and ensure that we are in compliance with all national standards for radiation safety. At the end of each exam that uses ionizing radiation, radiation dose measurements and compared to benchmarks for comparable exams. If measured doses for a particular exam exceed benchmarks, immediate notification of the appropriate staff responsible for overseeing radiation safety is triggered. All radiation-emitting equipment is also separately and regularly evaluated with testing equipment to ensure consistent safety and quality of radiological operation.

Training of technologists and radiologists

Ongoing education of all technologists and doctors in our department regarding the principles of ensuring “ALARA” (As Low As Reasonably Achievable) radiation dose is key to maintaining radiation safety and accreditation of our CT scanners from the American College of Radiology.

Radiation Protection Committee

We maintain a Radiation Protection Committee that oversees radiation-intense protocols, radiological practice, and education regarding imaging algorithms to minimize patient and staff exposure to radiation when possible.

Common Patient Questions

Should I be worried about having a CT scan?

Not if your doctor recommends it. The benefits of finding out what’s wrong almost always outweighs the small possible risks. Modern CT scanners are designed to use as little radiation as possible.

Are there other options besides a CT scan?

Sometimes, doctors can use tests like ultrasound or MRI. But those tests don’t work for every condition. Your doctor and radiologist will choose what’s best for you.

What are doctors doing to lower radiation exposure?

They use special tools and settings to use less radiation, adjust for your size and age, and check each scan to make sure it’s really needed.

How do I know if I really need a CT scan?

Ask your doctor:

• Why do I need this test?
• Are there other tests that could work instead?
• How will this scan help my treatment?

Are there other resources I can review to better understand CT scans, their benefits, and their risks?

Yes, here are some helpful online resources:

More information about medical radiation is available at the radiologyinfo.org website. 

RadiologyInfo: CT Scan Information

Image Wisely

Image Gently

Your safety is the top priority of UCSF’s Department of Radiology & Biomedical Imaging.  We know that our patients may be concerned about radiation exposure, and we at UCSF are too.  UCSF is a global leader in adopting practices for the reduction of radiation in all of our patients.

We invite you to learn about what we do to ensure your safety when we make images of your body in the UCSF Department of Radiology & Biomedical Imaging.