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Re: Mammo Effective Dose
Joel
I must respectfully take issue with you on this one. Firstly, if it should happen that only one organ/tissue is irradiated, then there would be nothing wrong, in principle, with multiplying that single, mean glandular dose by the tissue weighting factor (ICRP 26 is still in force in the USA), to arrive at a total effective dose equivalent (TEDE). This is true exactly because the TEDE is the sum of the EDE's to all the irradiated organs (and the DDE, in the occupational arena). So, all you're doing is adding zero (0) to whatever EDE you've arrived at for the organ/tissue of interest, since there are no other doses of significance. Actually, this is the norm in occupational work with radioiodines, because the doses to tissues other than the thyroid are negligible, and the weighting factor for the thyroid is so large. I do wonder about applying the weighting factor (WT) for the general population to the exclusively female subpopulation that is mammoed. Since the male breast is much less radiosensitive than that of the female, it would seem that, for this group, the factor is biased low.
Then, it is true that the EDE should not be used to estimate risks to a single individual. (I'm not sure how the MGD would be used, though, given that these are risks of stochastic effects.) It doesn't follow that the EDE is not a useful value, for patient education. It helps people to put a medical doses in perspective, if one can relate them, simply, to doses received during their everyday lives, e.g., external backgrounds, internal doses from the K-40 in the fruits and vegetables that are, reputably, so health-giving. Even if one were to misuse the EDE, by applying it to an individual (and, I assure you, it's done all the time), the risk/benefit ratio, where the benefit would be catching a tumor early, would be, clearly, very small.
Someone's probably going to question the meaningfulness of using an EDE derived for the general population for a medical subgroup (i.e. patients). Whatever the merits of that argument in other contexts, it seems to me that this case is not comparable, since essentially all women should be getting regular mammograms as a part of routine health-monitoring.
I shall now recline in my seat, put up my feet, and eagerly await the slings and arrows of my esteemed colleagues in cyberspace.
Cheers
cja
At 03:16 PM 10/19/99 -0500, you wrote:
>I think one should be extremely cautious when attempting to determine the
>effective dose for a single organ and single individual.
>
>First of all, ICRP's intention was that the effective dose concept be used
>for radiation protection purposes of populations exposed to radiation. The
>weighting factors for calculating the effective dose are, therefore, based
>on a reference population of equal numbers of both sexes and a wide range
>of ages.
>
>ICRP 60 states "The effective dose is the sum of weighted equivalent doses
>in ALL tissues and oragns of the body" which to my way of thinking means
>more than one type of tissue.
>
>The purpose of the effective dose is to be able to estimate a risk of fatal
>cancer which would be equivalent to the same dose if given uniformily to
>the whole body.
>
>If one is concerned about the risk of breast cancer then effective dose is
>not the metric of choice but one should be considering the mean glandular
>dose (MGD). The risk of a developing a fatal cancer can then be determined
>based on the MGD and the age at exposure.
>
> Joel
>
>Joel E. Gray, Ph.D., Consultant
>2804 Second Street Southwest, Suite 334
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>
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>e-mail joelgray@sprynet.com
>
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