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Submitted by Kazuko Ohno, n/a
   Commenting as an individual
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yThe problems of using the same unit Sv for equivalent dose and effective@dosez
Recently, people have been interested in the risk of medical radiation exposure as many patients have to undergo more than one procedure, some of these being high dose procedures like CT and interventional radiological procedure. Many a times, patients ask us the radiation dose in a particular procedure. It becomes difficult for a doctor and technician to explain the difference between mGy and mSv which patients want us to clarify. The quantity for radiation protection has to be well-known to general public.
But, using a same special quantity Sv for equivalent dose and effective dose loses uniqueness of quantity and also creates confusion among non-physicists.
In addition, people are confronted with interchanging use of mSv and mGy not knowing what dose one is referring to.
The average absorbed dose and an equivalent dose have the same numerical value. Furthermore, we usually take an incidence surface dose (ESD) when we control the patient exposure.
Further one needs much time for conversion from an equivalent dose to an effective dose. We usually use an incidence surface dose, an incidence skin dose, an equivalent dose of the purpose internal organs for explanation of a patient.

On the other hand, many patients do not understand that mSv has more than two units to represent. Patients interpret the quantity as an effectiveness dose that expressed in Sv.

Anyone goes through Internet and can get various kind of information.
It becomes easy for a patient and their family who worried about a risk of radiation exposure to know relations between an effective dose and a risk.
However, for common people, is not easy to understand mutual relations of various quantities with the same unit mark. In this reason, many patients misunderstand that their risk of radiation examination is higher than a fact, and sometimes they worry about their risk of the radiation exposure which they have already undergone..
I am a radiologist of a university hospital, and as a public information committee of Japan Radiation Society@(JRS), have to cope with questions from patients from all over Japan who are worried about medical radiation exposure. The number of such letters received currently exceeds 100 a year. In Japan nearly 80% people are educated and wish to know the radiation dose in different procedures. They are not satisfied with the remark that these are technical terms and cannot be explained easily. The following letter is one of the typical questions from a patient to JRS.


I took various kind of radiation examination. Head CT, barium of bowels and stomach. I am anxious about radiation exposure. On my investigation, the standard value of an exposure dose was different when I look at different websites. I do not understand which is true.
For example, barium of bowels, some website says 4mSv and the other is 50 - 200mGy. The numerical value and units are both different. I do not understand which numerical value should I take and which can be used to estimate risk. In addition, for head CT one was 0.5mSv and the other was 50mSv.
How much will each true numerical value imply in term of risk? Thanking you in advance. (38 years old housewife)

This ICRP main advice (2006), recommends absorbed dose and equivalent dose for patient radiation exposure in medical care. I think it is useful to break off current confusion. However, I can go step further more and think that it is necessary to improve a dose quantity for radiation protection to a thing easy to read for a person who is not a specialist.

I want the solution that a general person can easily understand and effective dose is different from an equivalent dose somehow.
This is a comment as a radiologist working in Japan (14,000 CT on stream).