Chapter Four

In the most recent President's Cancer Panel (PCP) report, chapter four covers the issue of radiation from medical sources, and tonight I want to offer a synopsis from the first part of that chapter which covers medical imaging and nuclear medicine.

I continue to read in the hopes of understanding this better myself so that I can share my new found knowledge. At times , while reading, I feared that I would instead only succeed in making it more confusing for all of us.

The upshot and upside is that there are initiatives in place to educate not only patients, but physicians, technicians and other health care professionals on the dangers of over exposure to medical radiation. As indicated in previous posts on this issue, machines need to be calibrated, and doses lowered. Additionally, this report states that newer imaging machines have built in sensors that can reduce the amount of radiation used based on organ and person size.

Of special concern has been reducing radiation to children. This is an issue for several reasons. One is that time of exposure is related to incidence of cancer, independent from frequency or amount. In other words, radiation causes damage and if that cellular damage is not corrected on a molecular level, then mutant cells continue to multiply over time and the more time they have - i.e 60 years of life vs 10 - the greater the chance that a cancer could develop. Secondly, children have smaller bodies to absorb the radiation, have more rapid cell changes at certain ages due to developmental issues, and if things don't get reined in, will have a life time of exposures that will accumulate.

Another concern is the increased risk of breast cancer. The PCP report notes that breast cancer from radiation is an "important and controllable risk factor." The problem is that any imaging of organs or bones beneath the breast can expose the breast to this known carcinogen. Bear in mind that a mammogram exposes the patient to approximately .4 mSv of radiation while a coronary angiography can expose the breast and heart to 16 mSvs.

The FDA is also working on a plan to have electronic or paper cards (smart cards) that we can use to keep up with all our imaging and dosing. This could reduce multiple scans of the same body part i.e lost records, patient recall, etc. There is also a program in the works that is intended to help patients talk to their doctors - much as I have suggested - why do I need this exam? Perhaps an alternative test can be used, such as ultra sound, MRI or a blood test. This is meant to address both sides of the unnecessary scan issue. The scans doctors order because they are afraid not to, and the ones they order because the patient insists that they do. One scientist from Columbia University suggested that a third of CT scans could be replaced by other tests.

Even though this chapter explains the different units of measurement with regard to ionizing radiation - it doesn't provide a layperson with the tools necessary to fully grasp what is measuring what. I can tell you with certainty that whether it is an mGy, mSv , rads or rems - MORE of any of them is what you are trying to avoid. It does seem like most measures come back to the Sievert and then the millisievert or mSv.

Several examples in the text use the mSv and that helps me make some good points. Remember there is no known safe dose of radiation - we just try to find what is sometimes referred to as the amount that will provide a result - the "as low as reasonably achievable" dose. Example one: the exposure to radiation from the atomic bomb(s) dropped on Hiroshima can be measured in mSv. It is expected that people were exposed to between 5 and 100 mSv. Regular xrays and mammograms expose people to less than 1mSv. CT scans will have a very wide range based on where the scan occurs, but also on the other factors which have been noted, so a coronary angiography CT can expose a person to 16 mSv and a PET scan even more. In nuclear medicine, where the radiation comes from within - i.e you take the radioactive isotopes into your body orally or through IV, the dose can be double that - esp. if the isotope is thallium 201. But I believe that my Aha moment really came when I read about the limits that are proposed for radiology technicians. Example two: there are two groups that cover this issue and the US one, OSHA allows workers to receive more annual and cumulative mSvs than the International Commission on Radiological Protection does. Well I think we should limit our exposure to the ICRP worker standard, at the very least (or most, depending how you look at that sentence!). So that is 20 a year and no more than 100 within 5 years. A chest CT may deliver 7 mSv with a range of 4-18. The virtual colonoscopy that I used to think was a neat idea, delivers 10 mSv with a range of 4-13. To learn more values, see chapter four of the current President's Cancer Panel annual report.

Ionizing radiation comes from other sources as well, but about 48% of it comes from medical exposure. In the 1980s the medical amount was closer to 15% and that is the concern - the growing concern, regarding cancer incidence from medical imaging and nuclear medicine.