Re: Gamma Radiation Treatment of Coronary Ateries

[bgb3@mhg.edu]

I am responding to the entire RADSAFE instead of just to Michael because there
seems to be general interest in the subject.  There are several radioactive
source strings that are being investigated.  The most promising seems to be
Ir-192.  We have treated over 600 patients with both in-stent restenosis and
de-novo stenosis with radiation.  The results have been highly  (60 to 80
percent compared to placebo) favorable.  We have also used Sr90/Y90 sources, Y90
sources, P32 sources and Re188 sources.  The predominately gamma emitting
sources seem to work best.  The best theory is that the gamma emitters
distribute their energy to the tissue in a more uniform fashion than the beta
particle emitters.  The betas deposit their energy in a much more non-uniform
manner, creating a restenosis pattern that looks on the angiogram like a tootsie
roll pattern (called the candy wrapper effect).  The restenotic areas are at the
distal and proximal ends of the irradiation pattern.  In the middle is a nice
healthy region of open artery.  The beta emitters are preferred because of the
limited dose to the patient, but the nonuniformity of the dose distribution and
the subsequent end effects appears to limit the effectiveness of the technique.
The gamma emitting source string gives the best result but there are many health
physics problems to deal with.  One, of course, is the dose to the patient
(about 10 rem whole body.  This dose is still lower than the typical dose from
an angioplasty procedure.  It's just that the treatment dose is another large
(?) dose to a patient that has already received two or more of these procedures
prior to volunteering for the endovascular brachytherapy treatment.  The
activities typically used for the various modalities range from 13 GBq to 20 GBq
for the Ir-192 source to about 3.7 GBq for the beta emitters.

Another advantage for the beta emitters is the length of treatment time.  For
the gammas the treatment time is about 20 minutes.  The betas require about 4
minutes.  However, the set-up time for the beta sources is about 20 minutes and
the set-up time for the gamma source is about 5 minutes.

The dose must be delivered to the artery wall to be effective.  The source
string is centered in an artery that is typically 2 mm in diameter.  In order to
deliver a dose of 14 to 16 Gy the source will deposit  over 30 Gy to the center
of  the artery.  Typically, the dose is specified at 2 mm from the source.

I have written several papers on the subject and given a dozen or so talks.  I
gave one talk at  the Philadelphia HPS Meeting.  If you are interested in more
details on the procedure let me know by email or telephone (or even snail mail)
and I'll be happy to forward you a copy of one of the papers.

Bill

Billy G. Bass, PhD
Radiation Safety Office, Washington Hospital Center
110 Irving Street,  Washington, DC  20010

e-mail     bgb3@mhg.edu
Telephone      (202) 877-8025


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