Wednesday, May 31, 2006

ALARA, not Alarm

Nice post over at Scan Man's Notes. He has an excerpt from an editorial in Applied Radiology by the Chief of Rads at Maryland, Dr. Mezrich.
The editorial comes as a response to recent fears that diagnostic tests such as CT scans may increase the likelihood of cancer. This can be of particular concern for tests performed in children, who will presumably have a longer time to accumulate radiation doses from subsequent radiological studies. At our institution we recently had a discussion regarding the doses of radiation used for tests such as CT scans and others that involve radiation exposure. ALARA is an acronym for "as low as reasonably achievable," in reference to the amount of radiation used for a particular diagnostic test. There are some excellent standards available that take into account a patient's weight (mass) and adjust the doses of radiation accordingly.
The crux of the editorial speaks to the way cells repair damage due to radiation. There are excellent mechanisms for this, as we have evolved in an environment with a substantial amount of radiation. The real question is determining the level of radiation in both time and intensity that will overwhelm our ability to repair damage. Dr. Mezrich makes a good argument for thinking that our bodies can deal with the level of radiation from most tests rather well, and that total radiation dose stretched out over a lifespan does not necessarily increase the risk of cancer. The excerpt concludes by mentioning the need for research to find this specific level of harmful radiation. I suspect that there isn't a single dosage point, but rather as with most other functions of our complex physiology, we will narrow it down to a range of radiation that, in most people, would be sufficient to increase the risk of cancer.
A good read on the subject, for those interested.


  • ALARA is used in civilian nuclear power too! Time Distance Shielding. Ahhh. The good ole days when none of my decision involved recommending that we kill people.

    By Blogger Jim Barton, at 5/31/2006 1:36 PM  

  • You know, I thought about including some information regarding nuclear power, or lessons learned by physicists performing experiments in an elevated radiation environment. You would think that we had figured out how much is too much by now. Clearly there is quite a gap between the doses that the Curie's used and what we use now. Also, we don't routinely tag kids with radiation sensors to determine their exposure levels. Hmm, maybe there is a grant proposal in this for someone...

    By Blogger Carlos, at 5/31/2006 2:02 PM  

  • Do you not track how much exposure they recieve based on how much you give them? I thought dentists keep track of your total dose from X-rays and whatnot.

    My lifetime exposure is just less than 1 Rem. When I was in the Navy that would mean I was kind of a sissy. The ALARA folks would not encourage such an interpretation, but they are all sissies.

    By Blogger Jim Barton, at 6/01/2006 10:11 AM  

  • Actually, no, there is no way to track the total exposure. It would be a nice feature to include in a comprehensive medical record, if you had one. I suspect that dentists can only tell the amount of radiation you've received at their office, not over the course of many years if you have been seen in different places. Thanks for the comment, Jim, I think I will write a post about yet another reason that we need to have a national portable medical record, be it RFID, web based as you can get with Medem ( or something entirely new.

    By Blogger Carlos, at 6/01/2006 3:21 PM  

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