Nuclear Medicine Safety: Are Radioactive Tracers Safe?

What Is Nuclear Medicine?

Nuclear medicine uses small amounts of radioactive materials called radiopharmaceuticals or radioactive tracers to diagnose and sometimes treat various medical conditions. By detecting where these tracers collect in your body, doctors can see how organs function and identify abnormalities that other imaging methods cannot detect.

Nuclear medicine is a specialized branch of medical imaging that provides unique information about both the structure and function of virtually every organ in the human body. Unlike conventional X-rays, CT scans, or MRI, which primarily show anatomy, nuclear medicine examinations reveal how organs and tissues are working at the molecular and cellular level.

The radioactive tracers used in these procedures are carefully designed compounds that travel to specific organs or tissues in your body. Once there, they emit small amounts of gamma radiation that special cameras can detect. These cameras create detailed images showing the distribution and concentration of the tracer, which helps doctors understand how well an organ is functioning or whether there are areas of abnormal activity that might indicate disease.

Common nuclear medicine procedures include bone scans to detect fractures or cancer spread, heart scans to evaluate blood flow and heart function, thyroid scans to assess thyroid activity, and PET scans that are particularly useful for detecting cancer and monitoring treatment response. Each type of scan uses different radiopharmaceuticals specifically designed to target particular organs or physiological processes.

How Radioactive Tracers Work

Radiopharmaceuticals are designed to mimic substances that your body naturally uses or processes. For example, a radioactive form of glucose (FDG) is used in PET scans because cancer cells typically consume glucose at a higher rate than normal cells. When this radioactive glucose accumulates in areas of high metabolic activity, it becomes visible on the scan, allowing doctors to identify potentially cancerous tissue.

The radioactive component of these tracers is carefully chosen to emit just enough radiation to create clear images while keeping your exposure as low as possible. Most tracers use isotopes with short half-lives, meaning they quickly lose their radioactivity and are eliminated from your body within hours to days.

Is Nuclear Medicine Safe?

Yes, nuclear medicine examinations are very safe. The radiation dose from radiopharmaceuticals is low, typically equivalent to 1-3 years of natural background radiation exposure. The diagnostic benefits of these examinations far outweigh the minimal risks, and our bodies are naturally equipped to handle and repair minor radiation-induced cell damage.

The safety of nuclear medicine has been extensively studied over many decades, and the consensus among medical professionals and radiation safety organizations worldwide is that these procedures are very safe when performed according to established guidelines. The International Atomic Energy Agency (IAEA), World Health Organization (WHO), and numerous national medical organizations have all concluded that the benefits of properly indicated nuclear medicine examinations significantly outweigh any potential risks.

To put the radiation exposure in perspective, we are all constantly exposed to natural background radiation from sources like cosmic rays from space, naturally occurring radioactive elements in the ground (such as radon), and even small amounts of radioactive potassium-40 in our own bodies and the food we eat. The average person receives about 2-3 millisieverts (mSv) of natural background radiation per year. A typical nuclear medicine scan delivers a similar dose, meaning the additional exposure is roughly equivalent to what you would naturally receive over 1-3 years.

Healthcare professionals who perform nuclear medicine procedures are bound by the principle of ALARA (As Low As Reasonably Achievable), which means they use the minimum amount of radioactive tracer necessary to obtain diagnostic information. Additionally, these examinations are only recommended when the medical benefit clearly justifies the procedure—in other words, when the information gained will meaningfully impact your diagnosis or treatment.

Understanding Radiation Risk

While any amount of radiation carries a theoretical risk of causing cell damage, the actual risk from diagnostic nuclear medicine procedures is extremely small. To understand this risk in context, it's helpful to compare it to other everyday activities:

• Flying in an airplane exposes you to cosmic radiation, with a cross-country flight delivering about 0.03-0.05 mSv
• Living in a brick or stone building slightly increases your radiation exposure from natural materials
• Eating foods like bananas, which contain potassium-40, contributes to your natural radiation exposure
• A nuclear medicine bone scan typically delivers about 4-6 mSv, while natural background radiation is 2-3 mSv per year

Our bodies have evolved sophisticated mechanisms to repair DNA damage caused by radiation and other environmental factors. Most minor cellular damage is quickly repaired or the damaged cells are eliminated through normal biological processes. Only in rare cases where damage is not properly repaired might there be a small theoretical increase in long-term cancer risk, and even this risk is very small compared to other cancer risk factors in daily life.

Can Nuclear Medicine Cause Cancer?

The risk of cancer from nuclear medicine examinations is extremely small. While radiation can theoretically damage cells, the doses used in diagnostic imaging are very low. Multiple studies have shown that not having a medically necessary examination poses a greater risk than the minimal radiation exposure from these procedures.

It is understandable that many people have concerns about radiation and cancer risk, as we know that high doses of radiation can indeed cause cancer. However, the relationship between radiation dose and cancer risk is not straightforward, especially at the low doses used in medical imaging.

At high radiation doses, such as those experienced by atomic bomb survivors or people involved in nuclear accidents, there is a clear and measurable increase in cancer risk. However, at the low doses used in diagnostic nuclear medicine—typically a few millisieverts—it becomes very difficult to detect any increased cancer risk because any effect is so small it is lost in the natural variation of cancer rates in the population.

Scientists use what is called the Linear No-Threshold (LNT) model to estimate cancer risk from low-dose radiation. This model assumes that any amount of radiation carries some risk, no matter how small. Using this conservative approach, the estimated lifetime risk of developing cancer from a single nuclear medicine scan might be increased by approximately 0.01-0.05%, compared to the general population's baseline lifetime cancer risk of about 40%. This means the absolute increase in risk is extremely small.

It's also crucial to remember that cancer is a complex disease with many contributing factors, including genetics, lifestyle, environmental exposures, and random cellular mutations. Radiation from a medical scan is rarely, if ever, the sole cause of any cancer. The decision to perform a nuclear medicine examination is made when the diagnostic information it provides will meaningfully benefit your health care—and avoiding a necessary test could mean missing a serious condition that might otherwise be treatable.

How Long Does Radiation Stay in the Body?

Radiation from radiopharmaceuticals typically leaves the body within 1-2 days, though this can vary depending on the specific tracer used. The radioactive material naturally decays and is eliminated through urine or bowel movements. Most people can resume normal activities immediately after the scan, including being around others.

The radioactive tracers used in nuclear medicine are designed to leave your body relatively quickly through two mechanisms: radioactive decay and biological elimination. Understanding these processes can help ease concerns about lingering radiation exposure.

Radioactive decay is a natural process where unstable atoms release energy (radiation) and transform into more stable atoms. Each radioactive isotope has a characteristic "half-life"—the time it takes for half of the radioactive atoms to decay. For most nuclear medicine procedures, isotopes with short half-lives are chosen specifically to minimize radiation exposure. For example, technetium-99m, one of the most commonly used isotopes, has a half-life of only 6 hours, meaning that half of the radioactivity is gone within 6 hours, three-quarters is gone within 12 hours, and virtually all of it has decayed within 48-72 hours.

In addition to radioactive decay, your body actively eliminates the tracer through normal biological processes. Most radiopharmaceuticals are excreted through urine, which is why healthcare providers often recommend drinking plenty of fluids after your scan and urinating frequently. This helps flush the tracer from your system more quickly. Some tracers may be eliminated through bowel movements or other routes, depending on their chemical properties.

Precautions After a Nuclear Medicine Scan

For most nuclear medicine procedures, you can resume normal activities immediately, including being around family members, friends, and the general public. The radiation levels from standard diagnostic scans are low enough that they pose no meaningful risk to people around you.

However, for certain procedures—particularly those involving higher doses of radioactive material or therapeutic applications like radioactive iodine treatment for thyroid conditions—temporary precautions may be recommended. These might include:

• Limiting close contact with pregnant women and young children for a specified period
• Sleeping in a separate bed from your partner for one or a few nights
• Flushing the toilet twice after urinating and washing your hands thoroughly
• Using separate towels and utensils for a short period

Your healthcare team will provide specific instructions based on the type of examination you've had. It's important to follow these guidelines, but also to understand that they are precautionary measures designed to minimize already-low radiation exposure to others.

What About Pregnancy and Breastfeeding?

Nuclear medicine examinations are generally postponed until after delivery to avoid exposing the fetus to radiation. However, if a doctor determines the examination is medically necessary during pregnancy, special protocols minimize fetal radiation exposure. For breastfeeding mothers, a temporary interruption may be recommended depending on the specific tracer used.

Pregnancy requires special consideration when it comes to medical imaging that involves radiation. A developing fetus is more sensitive to radiation than an adult because its cells are rapidly dividing and forming new organs and tissues. For this reason, nuclear medicine examinations are typically deferred until after the baby is born when there is no urgent medical need.

If you are pregnant or think you might be pregnant, it is essential to inform your healthcare team before any nuclear medicine procedure. In most cases, alternative imaging methods that do not use ionizing radiation—such as ultrasound or MRI—can be used instead. If no suitable alternative exists and the medical situation is urgent, the decision to proceed will be made after careful consideration of the risks and benefits.

When a nuclear medicine scan is deemed medically necessary during pregnancy—for example, if there is a serious condition that must be diagnosed or monitored—the procedure can often be modified to reduce fetal radiation exposure. This might involve using the minimum amount of tracer needed, choosing isotopes with shorter half-lives, or timing the scan to minimize exposure. Studies have shown that while there is a slightly increased theoretical risk of childhood cancer following fetal radiation exposure, this risk remains very small in absolute terms.

Breastfeeding Considerations

Radiopharmaceuticals can pass into breast milk, which means breastfeeding mothers may need to take temporary precautions after a nuclear medicine scan. The specific recommendations depend on which tracer is used:

• Some tracers: No interruption to breastfeeding is necessary because negligible amounts enter the milk
• Other tracers: A brief interruption (typically 12-24 hours) may be recommended, during which expressed milk should be discarded
• Radioactive iodine: A longer interruption or complete cessation of breastfeeding may be required for therapeutic doses

Your healthcare team will provide specific guidance based on the examination you're having. If you are breastfeeding, make sure to mention this before your scan so appropriate recommendations can be made.

Are Nuclear Medicine Scans Safe for Children?

Nuclear medicine scans are safe for children when medically necessary. While children are more sensitive to radiation than adults because they are still growing, healthcare teams use special protocols to ensure radiation doses are kept as low as possible. The examination is tailored to each child's size and weight.

Children differ from adults in several ways that are relevant to radiation exposure. They have a longer expected lifespan ahead of them, which means more time for any potential radiation effects to manifest. Their cells are dividing more rapidly as they grow, making them somewhat more susceptible to radiation damage. And their smaller body size means that a given amount of radioactive tracer will result in a proportionally higher radiation dose if not adjusted appropriately.

For these reasons, pediatric nuclear medicine follows the principle of "child-sizing" all procedures. This means that the amount of radioactive tracer given to a child is carefully calculated based on their weight and the specific examination being performed. Standardized dosing guidelines, such as those published by the European Association of Nuclear Medicine (EANM) and the Society of Nuclear Medicine and Molecular Imaging (SNMMI), help ensure that children receive the minimum dose needed to obtain diagnostic images.

Despite the increased sensitivity of children to radiation, it's important to recognize that nuclear medicine examinations are only recommended when they are expected to provide important diagnostic information that will benefit the child's health care. In many cases, these scans can detect conditions that would otherwise be difficult or impossible to diagnose, allowing for earlier and more effective treatment.

Parents can help by asking questions about why the scan is recommended, whether there are alternative tests that don't use radiation, and what steps will be taken to minimize their child's exposure. A transparent conversation with your healthcare team can provide reassurance and help you understand the benefits and any minimal risks involved.

What Happens After a Nuclear Medicine Scan?

After a nuclear medicine scan, you typically feel normal and can resume your usual activities. The radioactive tracer continues to decay and is eliminated from your body naturally. Drinking plenty of fluids helps speed up elimination. Your results are analyzed by a nuclear medicine physician and shared with your referring doctor.

The period immediately following a nuclear medicine scan is generally uneventful. Most people feel completely normal and experience no side effects from the procedure. The tiny amount of radioactive tracer you received is not enough to make you feel ill or cause any noticeable symptoms.

To help your body eliminate the tracer more quickly, you are usually encouraged to drink plenty of fluids in the hours after your scan. This helps flush the tracer out through your urine. For the same reason, urinating frequently is advisable, and some people are told to flush the toilet twice as a precaution (though the radiation levels are quite low).

There are no dietary restrictions after most nuclear medicine scans, and you can eat and drink normally unless otherwise instructed. If you received sedation for the procedure (more common in young children or anxious patients), you may need someone to drive you home and should avoid operating machinery or making important decisions until the sedation wears off.

Getting Your Results

After your scan, a nuclear medicine physician—a doctor specially trained in interpreting these images—will carefully analyze the results. This analysis takes time because the physician must compare your images to normal patterns, correlate findings with your medical history, and sometimes consult with other specialists.

The nuclear medicine physician's report is then sent to the doctor who ordered your scan, typically within a few days. Your referring doctor will discuss the results with you and explain what they mean for your diagnosis and treatment plan. If you have questions or concerns about your results, don't hesitate to ask for clarification.

What to Expect During a Nuclear Medicine Scan

During a nuclear medicine scan, you receive a small amount of radioactive tracer, usually by injection. After waiting for the tracer to distribute in your body (minutes to hours depending on the scan type), you lie on a scanning table while a specialized camera creates images. The process is painless and non-invasive.

Understanding what happens during a nuclear medicine scan can help reduce anxiety and ensure you're prepared for the experience. While specific procedures vary depending on the type of scan, the general process follows a similar pattern.

Before the Scan

Preparation requirements vary depending on the type of nuclear medicine exam. Some scans require fasting for several hours beforehand, while others have no dietary restrictions. You may be asked to avoid certain medications or caffeine. Your healthcare team will provide specific instructions when your scan is scheduled.

When you arrive for your appointment, you'll be asked to confirm your identity, provide your medical history, and answer questions about allergies, recent illnesses, and current medications. If you might be pregnant or are breastfeeding, this is the time to inform the staff if you haven't already.

Receiving the Tracer

The radioactive tracer is typically administered through a small needle in a vein in your arm, similar to having blood drawn. Some tracers may be given orally (swallowed) or inhaled, depending on the type of scan. The injection itself is quick and causes only minor discomfort.

After receiving the tracer, there is usually a waiting period—ranging from a few minutes to several hours—to allow the tracer to travel through your bloodstream and accumulate in the target organ or tissue. During this time, you may be asked to rest quietly, drink fluids, or in some cases, perform specific activities like walking.

The Imaging Process

For the scan itself, you will lie on a comfortable table that may move slowly through a large, ring-shaped camera (for PET or PET/CT scans) or beneath a camera head that may rotate around you (for gamma camera scans). The scanning cameras do not emit radiation; they only detect the radiation coming from the tracer in your body.

You will need to remain still during imaging to ensure clear pictures. The scan may take anywhere from 15 minutes to over an hour, depending on the type of examination. The cameras make some noise, but the process is painless. Some people find it helpful to close their eyes and relax or listen to music if permitted.