Radiation units: Absorbed, Equivalent & Effective dose

[Music] hi everyone my name is pauline and i'm a belgian nuclear medicine resident this video is about radiation units when i had to learn this i was so frustrated because i couldn't find any website or video where this topic was explained clearly so today i will try to explain it in the easiest way possible hopefully this will spare you the frustrations that i had before we start i just want to say that canada uses the international system of units for radiation measurements while the usa uses a mix of international and conventional units this can lead

to confusion so in the following explanation i will mainly focus on the international units when we discuss radiation we actually mean two general phenomena we have activity and exposure activity is basically just how much radiation is coming out of something whether it is particles or waves while exposure measures the effect of radiation on substances that absorb it let's start with activity activity is a measure of the rate of radioactive emission from a source the international unit of activity is the becquerel which is defined as one radioactive decay per second or the number of nuclei disintegrations

per second in other words the becquerel counts how many particles or photons are emitted per second by source an older and still often used measure of activity is the kuri and this equals 37 billion becquerels the concept of activity is independent of the type of emission as well as independent of the material the radiation is impacting in other words the absorbed dose tells nothing about the radiation dose that is actually absorbed by objects if we want to know this then we have to look at exposure radiation exposure is expressed in several ways in the next

couple of minutes we will talk about the absorbed dose the equivalent dose and the effective dose the absorptors gives the amount of radiation absorbed in a matter beard bone fat muscle or concrete irrespective of the effects this deposit has on the material but why do we deal with the absorptios we have just discussed radioactivity and the intensity of a radioactive source but a radioactive source represents no biological risk as a long as long as it is isolated from the environment however when people or another system are exposed to radiation energy is deposited in the material

and radiation dose is delivered it is therefore very important to distinguish between radioactivity of a radioactive source and the radiation dose which may result from the source the international unit of absorbed dose is the gray this is defined as the absorption of one euler of radiation energy per kilogram of matter let's give you an example an x-ray beam will be attenuated by absorption as it passes through the body so not all tissues within the beam will absorb the same dose the radioactivity or the emission from the source will be the same but the absorbed dose

will be much greater for the tissues near the entrance surface than for those deeper within the body another example if you have a ct of your upper abdomen the absorbed dose to your chest is very low because it has only been exposed to a small amount of scattered radiation on the other hand the absorptors to your stomach pancreas liver and other organs is the greatest because they have been directly exposed to the radiation absorbed dose is the amount of radiation energy absorbed in tissue however different types of radiation cause different levels of biological damage to

tissue absorbed dose doesn't tell you anything about the impact that the type of radiation has on that tissue because for example one gray of alpha radiation is more harmful than one gray of beta radiation to account for this we use the equivalent dose which addresses the impact that the type of radiation has on that tissue it uses radiation weighting factors for the different types of radiation for example gamma and x-rays have a weighting factor of 1 as do betas alphas have a weighting factor of 20 meaning they cause 20 times the biological damage of gamma

rays for the same absorbed dose the equivalent dose is expressed in a measure called a deceivered an equivalent dose of one sievert of alpha radiation will have the same biological effects as one sievert of beta radiation but the activity and the absorbed dose will be much lower for alpha radiation one important note because all radiation used in diagnostic medicine has the same low harm potential the absorbed dose and the equivalent dose are the same only the units are different the probability of a harmful effect from radiation exposure depends on what part or parts of the

body are exposed studies have shown that the risk of damage leading to cancer or serious genetic disease is greater than tissues where cells divide frequently for example bone marrow is much more radiosensitive than muscle or nerve tissue to obtain an indication of how exposure can affect overall health the equivalent dose is multiplied by a tissue weighting factor related to the risk for a particular tissue or organ here you see the different tissue weighting factors bone marrow colon lungs stomach and breasts are given a high factor of 0.12 because these are organs with a high risk

of radiation-induced fatal cancer the skin on the other hand is assigned a factor of 0.01 if more than one organ is exposed then the effective dose is the sum of the effective doses to all exposed organs here's an example to illustrate this let's say it is necessary to undergo a tired examination the measured absorption is 10 milligray the equivalent dose will be the same only the units are different because all radiation used in diagnostic medicine has the same low harm potential however the effect of those will be different we multiply 10 by 0.03 to become

our effective dose let's recap activity is a rate of radioactive emission from a source the absorbed dose is measured by what radiation does to substances it has nothing to do with the radiation itself the equivalent dose is based on the absorbed dose to an organ adjusted to account for the effectiveness of the type of radiation and finally the effective dose provides a way to convert the equivalent dose to specific organs into a common standard that can be used to assess overall risk for different patterns of exposure thank you so much for watching this video if

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