SNMMI and Safe/Beneficial Medical Uses of Radiation

What Is Nuclear Medicine? Nuclear medicine—a vital component of the rapidly emerging field of molecular imaging—is a medical specialty that uses small amounts of radioactive materials bound to special compounds (radiopharmaceuticals) in combination with imaging instrumentation that examine molecular processes in the body to detect and evaluate disease, such as brain disorders, heart disease and cancer. In addition, radiopharmaceuticals are used for therapy in the treatment of, for example, overactive thyroids and some cancers.

What Is Radiation? Radiation is simply a type of energy; the most familiar form of radiation is visible light (like that produced from the sun or a light bulb). Other forms, like X-rays and gamma rays, are employed in a number of beneficial applications, including medicine. Natural radiation exposure comes from the earth (rocks, soil) and outer space (cosmic rays). A small amount of radioactive material even exists naturally in our bodies. Every year, each person is exposed to this natural radiation and a variety of other sources, including household smoke detectors and color television sets. Air travel increases exposure to cosmic radiation due to the higher altitudes (less atmospheric shielding).

How Is Radiation Used in Nuclear Medicine? In a nuclear medicine diagnostic procedure, small amounts of radiopharmaceuticals are introduced into the body by injection, swallowing or inhalation. The amount of the radiopharmaceutical that is used is chosen to provide the lowest radiation exposure to a patient while ensuring an accurate medical evaluation. These radiopharmaceuticals are designed to go to specific organs (for example, the liver or the heart). A special radiation detector (scintillation camera) is used to obtain images of the distribution of the radiopharmaceutical in the body. PET (positron emission tomography) scans provide a means to study many types of disease in the body by determining how a disease uses radioactively labeled sugar, thus using the body's own processes to determine disease status.

What Levels of Radiation Are Involved With Diagnostic Nuclear Medicine Procedures? The amounts of radioactivity administered to the patient are relatively small and are designed to provide the highest quality diagnostic information possible while minimizing the radiation dose to internal organs. The radiation dose to different patients and internal organs varies with procedure. A typical nuclear medicine procedure may impart a radiation dose to the patient comparable to about one to four years of natural background radiation depending on the type of study.¹ As with X-rays, the value of diagnostic imaging is great and the risks are negligible compared to the health benefits of having the procedure.

How Do Nuclear Medicine Procedures Compare With X-Rays and CT scans? Nuclear medicine scans detect the radiation coming from a radiopharmaceutical that is inside a patient's body. In contrast, other imaging procedures (for example, X-ray and CT scan) obtain images by using machines that send radiation through the body. Nuclear medicine is also different from other imaging procedures in that it determines the presence of disease based on biological changes in tissue rather than changes in anatomy. Nuclear medicine procedures are among the safest diagnostic imaging exams available; the amount of radiation received from a nuclear medicine scan is comparable to that of many diagnostic X-ray and CT procedures.

*Radiation doses are estimated; obtained from various sources.

As a Patient, What Do I Need To Know? As with all medical procedures, the safety of nuclear medicine procedures is enhanced when patients are well informed about the particular test or treatment and there is a clear and open line of communication between patients and medical teams regarding safety and the treatment protocol. Patients should know what specific radiopharmaceutical—including what radioisotope—will be used in their treatment or procedure. All radionuclides have a "half-life," which is a time that it takes for it to decay away, so patients may continue to emit detectable levels of radiation for different periods of time after different treatments.

Diagnostic Tests

• Diagnostic nuclear medicine studies are performed with Tc-99m (technetium-99m), which should not be detectable—even by sensitive radiation monitors—three or four days after a test.
• Fluorine-18 (F-18), usually attached to glucose (FDG), is the most common radioisotope used with PET imaging; it should be undetectable one day after a test.
• Myocardial perfusion (blood flow) imaging can be performed with technetium-99m (Tc-99m), thallium-201 (Tl-201) or a combination of both. While Tc-99m is undetectable after only a few days, Tl-201 may remain detectable for 30 days.

Treatment or Therapy

• Iodine-131 (I-131), used to treat hyperthyroidism, thyroid cancer and lymphoma, may remain detectable for as long as three months after treatment.

How Can I Get This Information? SNMMI suggests that physicians and medical teams explain to patients the risks inherent in any nuclear medicine procedure with regards to radiation exposure to themselves and others and provide clear, safety instructions when discharged.

• Patients and health care providers should discuss how long patients may emit detectable radiation following treatment.
• Patients—especially if they are going to travel—should obtain a letter from their doctor that contains the following information: the patient's name, contact information for the testing facility, the name of nuclear medicine procedure, the date of the treatment or test, the radionuclide that was used, its half-life, its administered activity and 24-hour contact information.

Does Nuclear Medicine Save Lives? Yes. More than 20 million Americans benefit each year from nuclear medicine procedures used to diagnose and treat a wide variety of diseases. The use of radiation in these procedures—with low risks—offers a safe and cost-effective means to provide doctors with information that would otherwise require exploratory surgery, necessitate more costly and invasive procedures or simply be unavailable. The risks of not performing a needed medical exam are usually much greater than the risks of the radiation exposures associated with the exam.

Nuclear medicine can be used to

• determine whether or not organs are functioning normally,
• show whether the blood supply to the heart is adequate,
• detect cancers at an early stage,
• determine the extent of cancer and assess the response of cancer to treatment,
• discover whether the heart can pump blood adequately,
• identify abnormal brain lesions without exploratory surgery,
• detect whether the brain is receiving an adequate blood supply and if brain cells are functioning or not,
• check whether or not kidneys are functioning normally and whether the stomach is emptying properly,
• ascertain lung function and bone density and
• locate a bone fracture before it can be seen on an X-ray.

Related Resources
¹Health Physics Society: Radiation Exposure From Medical Diagnostic Imaging Procedures (fact sheet)
http://hps.org/documents/meddiagimaging.pdf

²American Nuclear Society: Radiation Dose Chart
http://www.ans.org/pi/resources/dosechart/

³Nuclear Regulatory Commission: Biological Effects of Radiation (fact sheet)
http://www.nrc.gov/reading-rm/doc-collections/fact-sheets/bio-effects-radiation.html

⁴U.S. Department of Energy, Office of Biological and Environmental Research, Office of Science, Ionizing Radiation Dose Ranges
http://www.remm.nlm.gov/IonizingDoseRanges_Rem_DOEChart.pdf (doses in millirems)
http://lowdose.tricity.wsu.edu/resources_pics/images/026_dose-ranges-sievert.jpg (doses in millisieverts)

⁵National Institutes of Health Office of Research Services (Radiation Safety Committee) "An Introduction to Radiation for NIH Research Subjects" [brochure, may be requested by phone at (301) 496-5774]
http://drs.ors.od.nih.gov/services/rsc/forms_index.htm

⁶SNMMI: About Nuclear Medicine
http://interactive.snm.org/docs/whatisnucmed.pdf

Additional Links
U.S. Department of Health and Human Services: Understanding Radiation
http://www.remm.nlm.gov/remm_RadPhysics.htm#understandingRelativeDoses

U.S. National Library of Medicine and National Institutes of Health: Nuclear Scans
http://www.nlm.nih.gov/medlineplus/nuclearscans.html