IT SEEMS LIKE PEOPLE are always being warned about the dangers of common products. Certain herbicides have been linked to lymphoma, sunscreen may be risky, and now radiation technology such as computed tomography (CT) is recognized as possibly carcinogenic.1-4 Is anything safe?
This article explores the issues surrounding radiation exposure and cancer risk.
Background
Radiation is defined as the emission of electromagnetic energy or subatomic particles. Ionizing radiation describes radiation that interacts with matter and creates ionization (see Key terminology). During ionization, an atom or molecule acquires a positive or negative charge by gaining or losing an electron, often causing chemical changes. This process can damage cellular DNA and result in cell death or mutations such as cancers.5
In healthcare, diagnostic tools such as X-ray, CT, and nuclear medicine all use ionizing radiation to produce images, whereas those such as MRI and ultrasonography do not.5 Discovered by Wilhelm Conrad Roentgen in 1895, X-rays used in CT and radiographic imaging pass through the patient to a film or detector.6 Today, these films and detectors have been replaced by specialized digital devices that reduce radiation exposure. This information, including the degree to which the X-rays were attenuated, is used to create images showing slight, reproducible differences.5
Nuclear medicine is an example of functional imaging using the tracer principle. Scintigraphic images are produced following the administration of a radiopharmaceutical. The radiographic tracer's mechanism of action determines where the drug accumulates in the body. The radioactive component allows providers and radiologists to measure delivery to various areas of the body and present this information in the form of images.7
A growing problem
But why has the carcinogenic effect of ionizing radiation become more of a problem recently? The answer is simple: Because this technology is increasingly performed. For example, approximately 70 million CT scans are performed each year.8,9 Many of these could be replaced by MRI or ultrasonography, which offer no radiation risk to patients.10
The recent focus on CT is due to higher levels of radiation exposure when compared with routine X-rays.11 For example, a CT of the chest has an exposure of 1.5 milliSieverts (mSv), which is the equivalent to 6 months' exposure to background radiation. On the other hand, a chest X-ray has an exposure of 0.1 mSv. Abdominal studies have greater exposures, with CT measuring between 10 and 20 mSv and X-ray studies measuring between 6 and 8 mSv. Eliminating just one CT scan can significantly reduce patient radiation exposure.1
Research involving survivors of the nuclear bombings of Hiroshima and Nagasaki in 1945 demonstrated that approximately 1 in 2,000 individuals will develop cancer from a 10-mSv radiation exposure, roughly equivalent to one CT scan.12,13 In general, the chance of an individual developing cancer in his or her lifetime is 1 in 5. About 2% of these cancers are caused by radiation. If a cancer develops, it will not do so for years or even decades after exposure. The risk of developing cancer from multiple radiation exposures, as from routine CT imaging, is unknown, but it increases with each subsequent scan. While the chance of developing cancer from a radiologic study is small, avoiding unnecessary exposure lowers the risk.12,13
Reducing exposure
To minimize risks, the goal is to reduce patient exposure to unnecessary radiation. An estimated 33% of CT scans are unnecessary.14 These may account for up to 29,000 cancers and 15,000 related deaths in the future.14 In its Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging, the FDA stated that "20%-50% of high-tech imaging procedures, such as CT scans, fail to provide information that improve patient welfare and therefore may represent, at least in part, unnecessary imaging services."15
Monitoring patient radiation exposure depends on the modality:
* In nuclear medicine, the quantity of radioactive drugs or radiopharmaceuticals determines patient exposure, which is measured in millicuries or becquerel and included in the report.14
* In CT, two values are used to report radiation exposure: CT dose index (CTDI), which is the standard measurement of CT radiation output, and dose length product (DLP), which accounts for the total based on the duration of the scan. These values measure exposure rather than absorption and should be reported as milligrays, an international unit of absorbed energy per tissue mass.
* Positron emission tomography and CT is a combination of nuclear medicine and CT and should include the quantity of radiopharmaceuticals used, as well as the CTDI and DLP of the CT.
No regulations require healthcare facilities or professionals to track or check patient exposure before a radiologic study is performed, and no single entity is responsible for tracking all procedures. Credentialing organizations may require information on patient exposures, but no other action is necessary. A healthcare institution may track exposure from procedures within that specific organization, but institutions cannot monitor exposure from services performed elsewhere. For example, CT may be performed at one healthcare facility, while nuclear medicine may be performed at another. As such, an individual's total exposure to radiation from imaging services will remain unknown unless he or she is monitoring it privately.16
Healthcare professionals are expected to weigh the pros and cons of imaging studies before ordering one. In today's healthcare environment, however, it is not simple. Insurance companies have their own guidelines for when different procedures may be ordered according to cost. As a result, situations may arise in which CT is required before MRI.
Nursing considerations
Fear of radiation and cancer risk should never prevent necessary imaging services. According to the FDA's Initiative to Reduce Unnecessary Radiation Exposure from Medical Imaging, justification and dose optimization are both crucial considerations.15
Justification. The benefits to the patient should always outweigh the risks of imaging studies. All methods that use ionizing radiation should be performed only when necessary to answer a medical question, help treat a disease, or guide a procedure. The patient's clinical indications and health history should be carefully considered before making referrals to radiology.15
Dose optimization. Imaging services should use adjusted techniques to administer the lowest necessary radiation dose for adequate image quality, diagnosis, and intervention. This is also described as as low as reasonably achievable.12 Factors for dose optimization include the patient's size and the anatomical area scanned.15
These procedures must be performed in facilities certified by the American College of Radiology, and all equipment should be properly maintained and tested.15
Healthcare professionals should be informed of all previous procedures, particularly those prescribed by different providers. Advise patients to keep their own records and request copies of all reports. Encourage them to ask questions regarding imaging services; for example, "I have had a lot of CT scans. Is another one really necessary? Will it increase my risk for cancer?" In these situations, the best response is that the information provided by the test is clinically necessary.
Nurses should encourage patients to discuss their concerns with the provider; specifically, to ask why a scan has been ordered and inquire about safer alternatives, such as MRI or ultrasonography.11 In addition, nurses can inform the CT or radiology department about the patient's concerns, as these professionals are best able to address them.
Safety for nurses
Unless they are present in the room during CT or an X-ray, nurses will not be exposed to radiation. To be in the room while imaging with ionized radiation is underway, nurses must be provided with proper shielding such as lead aprons and a thyroid shield. Nurses who are or may be pregnant should never be in the room during the procedure, although they can safely be in the room to prepare patients before the procedure (see Safety considerations for nurses).17
Weighing risks and benefits
Open communication between patients and staff regarding the risks of and rationale for imaging services that utilize ionizing radiation such as CTs is crucial. Nurses concerned about exposing either themselves or their patients to radiation can voice their hesitations to the nuclear medicine staff or the facility's radiation safety officer. Educational in-services may also be beneficial and appropriate.
Background radiation: The radiation that is naturally present in an environment.
Functional imaging: The production of images based on the function of the area in question, including the measurement of a tracer uptake or the mapping of an organ's electrical signals.
Ionizing radiation: Radiation that produces ions when it interacts with matter.
Nuclear medicine: An example of functional imaging that uses ionizing radiation and the tracer principle.
Tracer principle: Radioactive isotopes have the same chemical properties of nonradioactive isotopes and may be measured externally with the appropriate equipment.
Safety considerations for nurses20,21
Nurses should be aware that patients who have undergone a nuclear medicine procedure will be radioactive. The degree to which a patient is radioactive depends on the study being performed. For diagnostic procedures, however, the radiation level from the patient is negligible and not considered a hazard. Typically, nurses can reduce their exposure on the day of the procedure by:
* spending as little time as possible with the patient.
* keeping as much distance as possible from the patient.
* shielding themselves using objects to absorb the radiation and reduce exposure. Shields may include walls and doors, but lead aprons are not considered proper shielding with these patients. During normal patient care, pregnant nurses are not expected to exceed acceptable exposure limits. If possible, they should not be assigned to patients undergoing diagnostic nuclear medicine studies.
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