Re: Linear No-Threshold Hypothesis

[a.zapantis@qut.edu.au (Alex Zapantis)]

>     
>          The rates of damage (and repair) are not consistent with     
>          some known serious effects; that is, the tissue damage and   
>          subsequent death of persons exposed to radioactive sources   
>          (e.g. Mexico and Brazil) where the dose rates were not acute   
>          (hence the DNA damage rates are likely less than the         
>          spontaneous rate), yet over a period of many weeks to        
>          months, severe cell death occurred.  Maybe cellular division   
>          delay is a factor.

Are you referring to the teletherapy source which was "found" and the
incident in the irradiation facility? I would have categorised both of these
exposures as acute even though in the case of the teletherapy source, the
dose was delivered over a period of weeks (I think??!!). For exposures of
this magnitude, the primary mechanism for damage to cells would be due to
free radicals formed in the cells which then react with organic molecules
(via cellular water/oxygen to form, for example peroxides) in those cells
rendering them incapable of performing their required function and hence
causing the death of the cells. Typically stem cells are most
radiosensitive, hence they are killed off in greater numbers than the mature
cells. When the mature cells die of old age (for want of a better term),
they are not replaced as the stem cells are all dead. This results in moist
desquamation or necrosis a period of days to a couple of weeks after the
irradiation event. Of course, damage to DNA would also occur in the cells
however the other mechanism kills the cells before effects related to DNA
damage become evident (if they ever do!!).

That's how I thought it worked. Any comments, corrections etc ??

Merry Christmas to all


                I know that you believe you understand what you think I said 
                but I am not sure that what you heard is actually what I meant.

                        Alex Zapantis
                        Radiation Safety Officer                               
                        Queensland University of Technology          
                        Health & Safety Section                             
                        Locked Bag No.2
                        Red Hill Qld 4059
                        AUSTRALIA

                        Ph     : 61 7 3864 3566
                        fax     : 61 7 3864 3993
                        email  : a.zapantis@qut.edu.au