As in many aspects of medicine and medical imaging, there are numerous benefits but also risks associated with using CT scanners. One significant risk is the exposure to x-ray radiation and its long-term impact on patients. CT scans expose patients and, to some degree, clinicians, to a small, targeted amount of radiation. Computed tomography is a tool which includes special x-ray equipment to create images of structures inside of the body, allowing doctors to thoroughly look at internal organs, tissues, and blood vessels. During a standard x-ray, some diseases and injuries that may not be easily detected because of organs that overlap; whereas with a CT scan, doctors are able to see areas of the body that may not be seen with an x-ray. CT imaging is also used as the main tool to examine the stages of diseases or tumors, establish treatment plans including follow-up treatment cancer plans.
There are over 80 million CT scans performed in the United States every year2. This has increased a lot since the 1980s when three million scans were performed annually, but this upward trend indicates how revolutionary CT scans results have become. CT scans have various purposes including: helping to diagnose conditions, guide medical procedures, and monitor treatments’ effectiveness. CT scans have enhanced diagnosis and treatment options in extraordinary ways, especially in eliminating the need for invasive treatments and risky procedures. However, a CT scan exposes the patient's body to some radiation. The total radiation exposure coming from medical sources is up to 50%, CT machines alone account for 24% of all radiation exposure in the United States (according to a report by the National Council on Radiation Protection and Measurements in 2009.)
CT scans use “ionizing” radiation; this radiation is a type of energy released by atoms in the form of electromagnetic waves or particles. It is powerful enough to allow the CT scan to pass through a patient’s body to create clear images to a computer. Sometimes, patients may need a separate CT scan with “contrast” to show certain parts of the body more clearly on the images; patients may need to ingest the “contrast” orally or get a shot of it into their veins. The dose quantity of the ionizing radiation is directly related to the CT image quality and the diagnostic accuracy of a CT exam.
People are exposed to ionizing radiation in everyday life from natural sources, mainly from the sun and radioactive gasses that come from the breakdown of uranium in rocks, soil and water. These are called “background radiation” and can vary depending on where you live; for example people living in the higher parts of Colorado are exposed to more radiation than those living in an area closer to sea level. The total average radiation exposure that people experience is 3 millisieverts (mSv) per year, which has not changed for a while. However, the total radiation exposure in the US has doubled since 1980, and experts do believe it is due to increased use of medical imaging devices. The sievert (Sv) is the unit of effective dose that accounts for the type of radiation of tissues and organs; however, it is often more practical to use smaller units such as millisieverts (mSv). With higher doses and higher dose rates comes the risk of impairing functioning of tissues or organs, and producing skin redness, hair loss, radiation burns or acute radiation syndrome, which has a dose threshold of 1000 mSv. However, if the radiation dose is low and administered over a long period of time, the risk is substantially lower as there is more time to repair damage. Unfortunately, after the use of CT scanners, there is still a risk of cancer that could appear years later after treatment.
Epidemiology studies examine populations exposed to radiation, such as survivors of the 1945 atomic bomb blasts in Hiroshima and Nagasaki, and radiotherapy patients, which showed that there was a significant increase of the risk of cancer with doses above 100 mSv3. The Life Span Study (LSS) of the survivors of atomic bombs in Hiroshima and Nagasaki, 1945, have actually provided a lot of information analyzing the health effects of being exposed to radiation and have been used to compare to medical equipment radiation practices.
Nevertheless, since cancer risk associated with the radiation dose from CT scanners is not zero, reducing this dose and focusing on radiation safety in CT is a top priority in the CT scanner community. A tremendous effort has been spent to improve dose efficiency and optimization of CT systems, including improvements in the detector, collimator, and beam-shaping filters. All medical equipment companies must follow the guidelines for computed tomography dose and be compliant to protect the staff and patients. In order to protect the staff, it is critical to limit the amount of scans done per day and per year, as well as incorporate lead protection. For example, Neurologica's Omnitom is compliant with NEMA XR-29 and MITA Smart Dose, while also offering radiation dose structured reporting, pediatric and adult protocols, dose check and automatic exposure control. In order to protect the patient, it is at the forefront of the CT scan community to ensure that the lowest dose necessary is used while the required level of image quality is produced, which in turn enables the doctors to provide the best possible care and treatment for the patient.
Some examples of imaging procedures and their approximate radiation doses are :4
CT scanning equipment is always improving; and focusing on reducing radiation exposure is at the forefront of the scientific and medical community’s goals. With the everchanging computational power in the future, iterative reconstruction will be implemented to improve image quality while reducing radiation dose. CT scanners will remain a very powerful tool to establish accurate diagnostic results and detect abnormalities in the body including bone, soft tissues and blood vessels; and enable doctors to receive valuable information in order to give patients the best possible treatment.