For Referring Doctors
Even low levels of ionising radiation may have adverse health effects, of which carcinogenesis is of greatest concern. There is only limited human epidemiological data and biological investigations can be contradictory on the potential side effects of the radiation dose delivered during most diagnostic medical procedures. In the absence of directly applicable observational evidence, the rate of cancer induction at low doses and dose rates is estimated by extrapolation from observations conducted on subjects exposed to high doses of ionising radiation. The hypothesis that has been adopted by the major advisory bodies is the linearity hypothesis, according to which the increased risk is proportional to the excess radiation dose, including a dose and dose rate effectiveness factor of 2, which halves the risk per unit dose at low doses or low dose rates (or both). The overall consensus is that the risk for eventual fatal cancer is 0.05 per Sv of absorbed dose.
Much of the current understanding about the risk of exposure to ionising radiation for humans is based on the Life Span Study of the survivors of the bombings of Hiroshima and Nagasaki as reported by the Radiation Effects Research Foundation. The Life Span Study demonstrates that the risk of ionising radiation varies with both age and sex.
Younger subjects have a significantly higher risk than older subjects for most cancers as
- Actively growing tissue of younger subjects is more radiosensitive
- Younger subjects have a longer life span that allows for a longer time for the risk to manifest
- Radiation dose may be different in children as compared with adults due to patient size, organ size and orientation and organ distribution of administered contrast material
Girls demonstrated a higher risk for cancer induction than boys, which is in large part attributable to the excess risk of breast cancer.
CRITICAL ORGAN & EFFECTIVE DOSE
The risk depends on the dose delivered to each radiosensitive organ and the risk of cancer induction for that organ. The organ receiving the highest dose is referred to as the critical organ.
The effective dose is a commonly used dose metric. It is the weighted sum of the individual organ doses based on the biological radiosensitivity of each organ.
Affidea has developed a set of protocols that provide sufficient image quality with minimal risk to the patient. In general, the clinical benefits for patients of using appropriate imaging studies far outweigh any potential risk arising from the exposure to ionising radiation.
Communicating Radiation Risk
Media reports and the general public are increasingly interested in risks posed by patients’ exposure to ionising radiation from diagnostic medical procedures. There is particular concern for children because they are more sensitive to radiation than adults. It is extremely important that you, as a member of the patient care chain, be provided with the tools to effectively communicate with patients and families about the medical use of radiation, radiation dose and risks involved.
When patients ask about radiation dose, what they are really asking about is risk. It is no longer sufficient to indicate that these procedures are safe. Patients and their families need to be reassured, their concerns understood and their questions answered.
Experience has shown that patients can be provided with dosimetric and risk information, including a possible risk of developing radiation-induced cancer. Such information typically does not adversely affect the willingness to undergo an appropriate medical imaging test.
The most effective way to communicate radiation risk to the public continues to be a topic of discussion. One approach is to discuss with the patients and their families that radiation exposure from a CT scan has some risks, just like risks from other medical procedures, even prescription drugs. They can be told that radiation dose from these tests may slightly increase the risk of cancer induction. The risk is even higher in younger children, but is still very small.
It can be explained that the radiation dose from a CT is in a similar range as many other diagnostic imaging tests. It is also comparable to the exposure that individuals get from natural background radiation in 1 year. One can also compare the cancer risk associated with radiation exposure to the natural risk of cancer (1 in 1000 from CT, as opposed to 1 in 5 natural risk).