Re: dose calc

[John Moulder <jmoulder@post.its.mcw.edu>]

> A Dr. Howard Vogel told me recently that an experiment he did in Oak 
> Ridge several years ago showed that exposure of rats over a long period 
> of time caused much higher rates of mammary cancer than the same 
> exposure over a short period.

I'm not familiar with this work, and I can't find any reference to it in the 
literature.  However, Vogel is a well-known name in radiation carcinogenesis, 
although I haven't seen any publications in years.

In genera, the carcinogenic effects of ionizing radiation decreases with 
protraction.  For mammary cancer, however, both the laboratory and the 
epidemiological data indicate very little dependence on dose-rate 
(protraction).

> I thought a rem was a rem. If not what good is this method of 
> calculating the biological damage done to an organism? 

For the purposes of radiation protection a rem may be a rem, but from the 
point of view of radiation biology this is not so.  
1)  To convert a rad to a rem (or a Gray to a Sievert) you multiple by a 
Quality Factor.  But this quality factor is a approximation of reality.  The 
real measured quantity is the Radiobiological Effectiveness (RBE, the dose to 
produce an effect with 250 kV X-rays divided by the dose to produce the same 
effect with some other type of radiation).  For a given type of radiation RBE 
depends on the cell or tissue type, the total dose, the dose rate and the 
endpoint.  Thus equal rems do not produce equal effects if you look at 
different schedules, endpoints, etc.
2)  Dose rate (dose/unit time) and fractionation (number of radiation 
sessions), as well as total dose, affect most biological endpoints.  So that 
equal rem of the same king of radiation produce different effects when given 
in different schedules.

I think the key is to not confuse the regulatory/legal aspects of _radiation 
protection_ with the research/science issues of _radiation biology_ and 
radiation physics.

John Moulder (jmoulder@its.mcw.edu)
Radiation Biology Group
Medical College of Wisconsin