DNA damage from low-LET radiation

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

I recently read a letter by John Wards in Radiation Research (1991)
discussing qualitative differences in DNA damage caused by radiation as
opposed to other mutagens. It sounds as though he is saying that even
low-LET radiation causes DSBs, which is contrary to what I had always heard.
This suggests to me that the difference in radiation "quality", then, would
stem from the number of DSBs a particular radiation causes.  Is anyone
familiar with this letter or the underlying research?  Would it be accurate
to say that all radiations cause DSBs, but that high-LET radiations have a
higher probability of causing them in any particular cell, accounting for
the higher RBE of alpha and neutron radiation? Also, is it still safe to say
that much damage from low-LET radiation is indirect, caused by free radical
formation within the cell and that this process is enhanced by the
occasional DSB?  Can anyone suggest to me further reading that might help to
better explain this to me?
This interests me for the following reasons:
It seems contrary to what I understood to be conventional wisdom regarding
the nature of damage from low-LET radiation
If there is a qualitative difference between damage due to low-LET radiation
and other mutagens, this suggests to me that there may be similarly
qualitative differences between mechanisms to repair radiation damage as
compared to other DNA damage
I would greatly appreciate any information or references anyone may care to
offer.  Thanks!
Andy
P. Andrew Karam, CHP
Radiation Safety Officer
University of Rochester
(716) 275-1473 (voice)
(716) 256-0365 (fax)
andrew_karam@urmc.rochester.edu 

There is no Chase so pleasant, methinks, as to drive a Thought, by good
conduct, from one end of the World to the other; and never to lose sight of
it till it fall into Eternity, where all things are lost as to our
knowledge.    T. Burnet, The Theory of the Earth, 1697

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