Radiation exposure in thoracic imaging

Most thoracic imaging requires exposure to ionising radiation. Effective dose (measured in sievert [Sv] or millisievert [mSv]) is a radiation protection quantity defined by the International Commission on Radiological Protection. It is used to measure ionising radiation in terms of the potential for causing harm. It takes into account not only the actual dose of radiation absorbed by the body, but also the radiosensitivity of the exposed organs or tissues, and the specific form of radiation in question (eg computed tomography [CT] vs nuclear medicine). The actual effective dose of radiation from an imaging investigation varies greatly with patient size, technical factors (eg scan coverage) and local scanner protocols. Effective doses included in this topic are used for reference and allow comparison of different imaging investigations. Note that radiation exposure also arises from various natural sources including cosmic and terrestrial. The average annual natural background radiation in Australia is approximately 2 mSv.

Health risks from radiation doses used in routine medical imaging are too low to be detectable and may be nonexistent. Nevertheless, the aim is to expose patients to the lowest reasonably achievable radiation dose without unacceptable loss of image quality. Choose the imaging investigation that provides the greatest amount of diagnostic information, so that theoretical risks from radiation are outweighed by the benefit of the imaging investigation; consult radiologist for advice if required. To avoid unnecessary radiation exposure, imaging investigations should be performed at appropriate intervals and not repeated unless warranted.

Children are more sensitive to ionising radiation; if a computed tomography (CT) scan is considered in a child, consult with a paediatric specialist.

Breast tissue has relatively high radiosensitivity, particularly in younger or lactating women.