[ RadSafe ] Re: radsafe Digest, Vol 181, Issue 3

[Dale Boyce]

Optimal half-lives for diagnostic radiopharmaceuticals is comparable to the 
localization time. That said, it isn't always possible. Since there are a 
limited number of candidates compromise is the name of the game.

With a half life of 6 hours Tc-99m and its various chelating agents 
localizes fast enough to allow enough activity to be administered to allow 
relatively rapid imaging. I-123 localizes sufficiently rapidly to allow its 
use for imaging thyroid and thyroid CA mets.  Most other diagnostic and 
therapeutic isotopes are around 3 days.

The currently defunct Ho166 treatment of multiple myeloma was 26 hours to 
shorten the time the patient could undergoe autologous stem cell transplant. 
Otherwise, the ~3 day Y-90 would have been a better choice for better dose 
to non-target/target ratio.

Three days is sort of a default half-life that optimizes the initial dose 
activity, localization, imaging speed, and dose to non-target tissue. Oh, 
and yeah, the ability of a manufacturer to economically distribute the 
isotope.

PET isotopes are sort of a wild card. The high dose due to the positron 
requires a very short half-life to get a reasonable imaging time without too 
high a dose to the patient. Fortunately, PET isotopes/radioparmaceuticals 
are chosen that image and decay very rapidly.

Dale


----- Original Message ----- 
From: "Ed Stroud" <estroud at smtpgate.dphe.state.co.us>
To: <radsafe at radlab.nl>; <al at solidsurfacealliance.org>
Sent: Monday, January 26, 2009 6:09 AM
Subject: [ RadSafe ] Re: radsafe Digest, Vol 181, Issue 3


Most cardiac stress tests use Tc-99m with a half-life of 6 hours. However, 
some cardiologists prefer to use a combination of Tc-99m and Tl-201. 
Thallium has a half-life of 73 hours.
-Ed Stroud

>>> <al at solidsurfacealliance.org> 1/23/2009 5:30 PM >>>


Hi All,

I friend of mine had a stress test on Tuesday, heart patient, had some 
stents installed a few weeks back.   About a foot away from his chest, my PM 
1703 Gamma Scintillator was reading over 2,500 uR/hr.   This was Saturday 
night, at least four full days after the procedure.

Is this unusual?  I thought most of those medical isotopes had very short 
half lives.

Thanks,

Al

_______________________________________________
You are currently subscribed to the RadSafe mailing list

Before posting a message to RadSafe be sure to have read and understood the 
RadSafe rules. These can be found at: 
http://radlab.nl/radsafe/radsaferules.html

For information on how to subscribe or unsubscribe and other settings visit: 
http://radlab.nl/radsafe/

_______________________________________________
You are currently subscribed to the RadSafe mailing list

Before posting a message to RadSafe be sure to have read and understood the 
RadSafe rules. These can be found at: 
http://radlab.nl/radsafe/radsaferules.html

For information on how to subscribe or unsubscribe and other settings visit: 
http://radlab.nl/radsafe/


-- 
Internal Virus Database is out-of-date.
Checked by AVG.
Version: 7.5.552 / Virus Database: 270.10.10 - Release Date: 1/19/2009 12:00 
AM