The committed effective dose, denoted as , is a fundamental quantity in radiological protection, specifically designed to quantify the long-term health risk associated with the intake of radionuclides into the body. Defined by the International Commission on Radiological Protection (ICRP), it represents the sum of the committed equivalent doses to all organs and tissues of the body, each weighted by its respective tissue weighting factor, accumulated over a specified integration time following an intake.
Unlike the effective dose which characterises the stochastic health effects from external exposure or an instantaneous internal exposure, the committed effective dose accounts for the dose accumulated internally over an extended period. This is particularly relevant because radionuclides deposited within the body continue to irradiate tissues and organs as they decay and are metabolised. The primary purpose of this quantity is to provide a single, comprehensive measure of potential long-term harm from internal contamination, enabling comparison with doses from external sources and facilitating the establishment of regulatory limits for radionuclide intakes.
The calculation of committed effective dose involves several key steps, based on the principles outlined in ICRP publications. The general formula is expressed as:
Where:
The committed equivalent dose, , is the time integral of the equivalent dose rate, , in a specified tissue or organ following an intake of radioactive material. It is calculated as:
Here, is the time of intake, and is the integration period over which the dose is summed. This integration accounts for the protracted nature of internal exposure as the radionuclide moves through and is eventually eliminated from the body, whilst undergoing radioactive decay.
Tissue weighting factors () are dimensionless quantities published by the ICRP that reflect the sensitivity of different tissues and organs to the induction of stochastic effects (e.g., cancer, hereditary effects). These factors are crucial for converting organ-specific equivalent doses into a whole-body effective dose equivalent, allowing for a normalised assessment of risk irrespective of the specific tissues irradiated.
The choice of integration time is critical. For occupational exposure to adults, the ICRP generally recommends an integration period of 50 years. For members of the public, particularly for children and infants, an integration period of 70 years is used to account for their longer life expectancy post-exposure and potentially greater radiosensitivity. This ensures that all significant doses received over a typical lifetime are included in the assessment.
The committed effective dose plays a central role in several aspects of radiological protection, including the assessment of doses from accidental intakes, the setting of annual limits on intake (ALIs) for occupational workers, and the evaluation of environmental contamination scenarios. Its use ensures a consistent and conservative approach to quantifying long-term health risks from internal radiation sources, underpinning the ALARA (As Low As Reasonably Achievable) principle for dose optimisation programmes.
For further details and specific definitions, refer to the following ICRP publications: