[ RadSafe ] AW: medical issues

[Franz Schönhofer]

Mike,

Thank you very much for your comments. My only excuse is that I only
regarded Cs-137 from the Chernobyl accident. I know that clinical
administrations of other radionuclides might be quite different regarding
compounds and other circumstances. I think that we share the common
knowledge that Cs-137 is not used in vivo, because there is no application
for it. Its metabolism has been more than extensively researched in
post-Chernobyl publications.

Your further explanations to my question on the impurities I have to check
separately- it is rather close to midnight in my middle 
European Time Zone...

Thanks again!

Franz



Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna
AUSTRIA


-----Ursprüngliche Nachricht-----
Von: Stabin, Michael [mailto:michael.g.stabin at Vanderbilt.Edu] 
Gesendet: Dienstag, 27. Jänner 2009 21:56
An: Franz Schönhofer; radsafe at radlab.nl
Betreff: RE: medical issues

> The biological half-lives of radionuclides like Cs-137, Tl-201, Tc-99m and
all others can be easily found within a minute at Google

Well, not really, if you account for the many different compounds that the
nuclides may be labeled to. The elemental forms, yes, but Tc-99m is labeled
to dozens or hundreds of compounds, each of which has its own unique
metabolism. This has been well characterized by the ICRP Task Group on
Radiopharmaceutical Dosimetry, and we at RADAR try to keep their
recommendations updated on our website (www.doseinfo-radar.com, see the
nuclear medicine pages).

> What I am rather surprised is, that so much "radioactivity" should be
attributed to impurities in the radionuclides used. To my knowledge there
are usually limits set for the concentration of long-lived radionuclides in
the production - of course on radiation protection grounds.

In nuclear medicine, the levels of activity are higher than many are used to
dealing with in other areas of health physics, as the half-lives are shorter
(remember, Cs-137 is not a nuclear medicine nuclide), and the radiation dose
per unit activity is much lower. High levels of activity are used to produce
as high a quality of image can be obtained (typically hundreds of MBq), or
in therapy to deliver high doses to malignant tissues (high numbers of GBq).
In medicine, there are no legislative limits on radiation dose for patients.
Radiopharmaceuticals are approved (in the USA) by the Food and Drug
Administration, and physicians can vary the amount of activity, and thus
radiation dose, given to any patient within reasonable limits to ensure that
good medical information is obtained to diagnose or treat disease.
Impurities in radiopharmaceutical products are tolerated to certain levels,
and watched closely. For years we had a lot of I-124 in I-123 products,
which is problematic dosimetrically. The I-123 production methods were
changed, and this situation was significantly improved. The contaminants in
Tl-201 products are quite detectable, but don't contribute all that much to
radiation dose, see for example J Nucl Med. 46(3):502-508, 2005.
Contaminants in In-111 products were once quite a dosimetry issue for
labeled blood cells (J Nucl Med 26:1090 1093, 1985), but now Tc-99m labeled
products have taken over much of these imaging studies.

By the way, I would like to endorse again the excellent analysis by Pat
Zanzonico of the Memorial Sloan Kettering Cancer Institute on the possible
numerical **benefits** of medical examinations involving radiation, see
http://hps.org/hpspublications/articles/Benefitsofmedradexposures.html. My
name only appears on this because I helped organize the web page, the
brilliant analysis was all written by Pat.


Mike
 
Michael G. Stabin, PhD, CHP
Associate Professor of Radiology and Radiological Sciences
Department of Radiology and Radiological Sciences
Vanderbilt University
1161 21st Avenue South
Nashville, TN 37232-2675
Phone (615) 343-4628
Fax   (615) 322-3764
e-mail     michael.g.stabin at vanderbilt.edu
internet   www.doseinfo-radar.com
 
"I am realistic -- I expect miracles." - Wayne Dyer