by Leif Kullman
Radiation safety again
Radiation safety matters are always important and our patients are sometimes worried.
Unfortunately, they are also very difficult matters, it is difficult to get a final answer for many of them. They are also interesting for our daily newspapers and today I would like to report from an article in New York Times November the 27, written by Gina Kolata. The name of the article was: ”For radiation, How much is Too Much?”
Federal agencies seem to be in quandary in US today, because they have found
out that radiation from natural sources are much, much larger than the ones
coming from human efforts. Natural sources can be cosmic rays, radon seeping
out of the earth and radioactive substances in soil, water, food and even
from potassium in the human body itself.
Up to today regulators have acted as if every bit of excess of radiation
exposure is potentially hazardous, but today the same regulators have to
admit that they are regulating doses that are lower than the natural
background of radiation.
Also the situation is getting more confused, according to experts since the
regulatory standards are a hodgepodge. As for one agency, the Environmental
Protection Agency advocates a standard for all radiation exposure from a
single source at 15 millirem a year. A standard chest x-ray, in comparison
gives about 10 millirem to the chest. But the Nuclear Regulatory Commision
sets its acceptable level of radiation exposure from any source at 25
millerem a year. In contrast to this, the natural level of background
radiation in US, on average, is about 350 millerem a year and even higher
than that in some areas of the country.
As mentioned one natural radiation source is cosmic rays and in New York,
for example, people absorb about 100 millirem each year of this radiation
and in Denver, which is situated in a higher altitude, exposure from cosmic
rays averages 200 millerem every year. In addition to that, we also know
that mankind eat, breathe and drink low levels of radiation.
So if we look at the exposure of the population from radiation, about
two-thirds is due to natural background and only about 15 %is due to medical
sources (including dentistry).
Risk analysts have now been involved and scientists say that the quandary
over how to set radiation levels does not result from a lack of research or
analysis. Radiation´s effects on people have been studied a lot and in US a
lot of agencies and committees are involved. As with other substances in the
environment, the costs are high to keep up good standards.
Scientists rely on a mathematical model in estimating radiation risk. The
most widely used model is known as the linear-nontreshold dose-response
model. It assumes that there is no safe dose of radiation and that the risk
of getting cancer or a genetic damage increases along with radiation
exposure.
But other researchers disagree a little and say that there is, in fact, a
treshold below which radiation poses no hazard to health. And still others
say that low doses of radiation are actually beneficial.
And while the scientists
are arguing, the regulatory agencies continue to disagree on radiation
standards in US. Lately a new report from the National Council of Radiation
Protection and Risks came. It recommended the linear model, saying that
there is no conclusive evedence on which to reject the model.
