Mice Irradiation Questions

[Erick Lindstrom <avrel@gemini.oscs.montana.edu>]

Dear Radsafers:

A researcher here at Montana State University has proposed to irradiate a
few dozen mice to 500 rads each.  The purpose of this exercise is to enhance
post-irradiation implanted tumor growth (due to immunosuppressive and other
radiation induced factors).

Most of the literature that we are looking at does not describe the dose
rate used in preparing mice for tumor implantation.  Nearly all indicate a
dose of 500 rads, although one article suggests a dose of 150 rads given at
a dose rate 70 rads/min.

My question is:

How critical is the "acuteness" of the dose given to the mice (in order to
achieve the desired effect).  Given target uniformity considerations, the
highest dose rate I can produce with our "irradiator" (naval radiac
calibrator AN/UDM-1A) is a little over 8 rads/minute.  That gives us an
irradiation time of about an hour to reach the 500 rad dosage (yes, we've
run this by the Animal Subjects Committee!).  Design complications of the
"container" in which the mice will be irradiated may necessitate longer
irradiation periods.

Obviously, before we proceed we want to be reasonably confident that we'll
obtain positive results.  For those who have experience in this area, will
our system work (or will the dose rate limitation compromise this undertaking)?

One more question:

There are mice available that have been bred to express immunodepression
(apparently there are some transgenic lines available as well).  However,
despite the phenotype, these mice do not sustain and promote implanted tumor
growth as well as mice that have received significant doses of radiation.
Not having explored this realm of radiation biology much, what "other
radiation induced factors" are at play here?

Thanks for your help!

-Erick Lindstrom

 Erick Lindstrom
 Radiation Safety Officer
 309 Montana Hall
 Montana State University
 Bozeman, MT  59717-0244
 Phone: (406) 994-2108
 Fax:	(406) 994-4792
 avrel@gemini.oscs.montana.edu