Effective Dose
The relationship between the probability of stochastic effects and equivalent dose is found to depend on the organ or tissue irradiated. To account for this, tissue weighting factors \( w_T \) are introduced. These factors represent the relative contribution of an organ or tissue \( T \) to the total detriment due to the stochastic effects resulting from a uniform irradiation of the whole body.
The total tissue-weighted equivalent dose is called the effective dose, and is defined as:
\[ E = \sum_T w_T H_T \]
Where:
- HT is the equivalent dose in organ or tissue \( T \),
- wT is the tissue weighting factor for organ or tissue \( T \),
- The sum is performed over all organs and tissues of the human body that are considered to be sensitive to the induction of stochastic effects.
Recommended tissue weighting factors can be found in ICRP Publication 103. Despite being dependent on the sex and age of the person, for radiation protection purposes, the values for tissue weighting factors are typically taken as constants, applicable to the average population.
The use of effective dose has many advantages in practical radiation protection. It allows for very different exposure situations (such as internal and external exposure by different types of radiation) to be combined and represented by a single value: the effective dose.
Summary of Radiation Protection Quantities and Units
| Quantity | Unit | Description |
|---|---|---|
| Mean Organ Dose (DT) | Gray (Gy) = J/kg | Measures the energy imparted to a specific organ or tissue from radiation. |
| Equivalent Dose (HT) | Sievert (Sv) | Accounts for the biological effectiveness of different types of radiation. |
| Effective Dose (E) | Sievert (Sv) | Summation of the equivalent doses to various organs, weighted by tissue sensitivity. |
| Ambient Dose Equivalent (HA) | Sievert (Sv) | Measures the radiation dose in the environment. |
| Personal Dose Equivalent (HP) | Sievert (Sv) | Monitors the dose received by an individual from external radiation sources. |