The key difference between absorbed dose and equivalent dose is that absorbed dose is the measure of the energy deposited by radiation in a mass, whereas equivalent dose is calculated for individual organs.
We can describe radiation dose as the amount of exposure to radiation. There are three kinds of doses in radiological protection: absorbed dose, equivalent dose, and effective dose.
CONTENTS
1. Overview and Key Difference
2. What is an Absorbed Dose
3. What is an Equivalent Dose
4. Absorbed Dose vs Equivalent Dose in Tabular Form
5. Summary – Absorbed Dose vs Equivalent Dose
What is an Absorbed Dose?
Absorbed dose is the total amount of energy deposited by radiation in a mass. This mass can refer to anything, such as water, rocks, air, people, etc. We can express the absorbed dose in milligrays (mGY). This dose assesses the potential for biochemical changes in specific tissues.
X-rays are different from sunlight and are able to penetrate deep into the body while depositing energy in the internal organs. Moreover, X-rays can even pass through a person’s body. The absorbed dose can determine the intensity of the energy deposited in any small amount of tissue located anywhere in the body.
The denotation absorbed dose is given by D. The SI unit is Gray and the other unit is Rad for representing the absorbed dose. The SI base unit for absorbed dose J.Kg-1. This term absorbed dose is usually used for calculating the dose absorbed by living tissue in both radiation protection and radiology. Moreover, we can use it directly to compare the effect of radiation on inanimate matter, including radiation hardening.
What is an Equivalent Dose?
The equivalent dose is the dose calculated for individual organs. This dose is depending on the dose absorbed by an organ, adjusted to account for the effectiveness of the type of radiation. Moreover, this dose is expressed in millisieverts (mSv) to an organ. This equivalent dose is useful in assessing how much biological damage is expected from the absorbed dose.
This amount takes the damaging properties into account of different radiation types. Since all radiation useful in diagnostic medicine has the same low-harm potential, the equivalent dose and absorbed dose are numerically the same. However, they have different units. The SI unit of the equivalent dose is Sievert.
The ICRP (International Commission on Radiation Protection) has designated the equivalent dose as a limiting quantity. This specifies the exposure limits, ensuring that the occurrence of stochastic health effects can be maintained below unacceptable levels and tissue reactions are avoided. Practically, an equivalent dose cannot be measured; thus, it is a calculated value. The purpose of this calculation is to generate a value comparable to the observed health effects.
When calculating the equivalent dose, we can use the mean absorbed dose that is deposited in body tissue or organ T, which is multiplied by the radiation weighting factor WR that is dependent on the type and the energy of the radiation R. Generally, radiation weighting factor represents the relative biological effectiveness of the radiation. It modifies the absorbed dose in taking account of the different biological effects with regard to the various types and energies of radiation.
What is the Difference Between Absorbed Dose and Equivalent Dose?
Absorbed and equivalent dose are important in measuring exposure to radiation. Therefore, the key difference between absorbed dose and equivalent dose is that absorbed dose is the measure of the energy deposited by radiation in a mass while the equivalent dose is the measure of an average absorbed dose in tissues and organs. Since all radiation useful in diagnostic medicine has the same low-harm potential, the equivalent dose and absorbed dose are numerically the same. However, they have different units.
Below is a summary of the difference between absorbed dose and equivalent dose in tabular form for side-by-side comparison.
Summary – Absorbed Dose vs Equivalent Dose
Therefore, the key difference between absorbed dose and equivalent dose is that absorbed dose is the measure of the energy deposited by radiation in a mass while the equivalent dose is the measure of an average absorbed dose in tissues and organs.
Reference:
1. Radiological Society of North America (RSNA) and American College of Radiology (ACR). “What Is Radiation Dose?” Radiologyinfo.org.
Image Courtesy:
1. “Dose quantities and units” By Doug Sim – Own work (CC BY-SA 3.0) via Commons Wikimedia