Re: Radioactive tissues

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Date:Wed, 08 Sep 1999 21:14:48 -0400 (EDT)
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Mark Lewis at Shandon asks:
>>processing tissues that have been labeled with radioactive isotopes? If so, 
did you have to dispose of the processing reagents as radioactive waste?<<

And Joseph Nocito at the Santa Rosa in downtown San Antonio (hey, I used to 
be at the Nix Hospital, a LONG time ago) replies: 

>>Our nuclear medicine departent has a procedure which they use technetium 
99m sulfur colloid to label sentinel nodes. We place the specimen in an ice 
chest, in a store room for 3 days before it is grossed. The half-life is 2.5 

As it looks like sentinel node biopsy is likely to become the standard of 
care in breast cancer and melanoma, this problem will become more common. 
(The tumor site is injected with technetium 99m sulfur colloid, and the first 
lymph node that takes up the radiopharmaceutical is biopsied.)

I reviewed this subject with several pathologists and nuclear medicine people 
on the PATHO-L mailing list a couple of years ago. They uniformly said that 
no precautions at all are necessary, and that the specimen may be processed 
promptly with no special safeguards. This is important to know, since the 
pathologist will under pressure for rapid turnaround in these cases, 
including probably some frozen sections (which medically are NOT advisable).

Technetium 99m is prepared by eluting from a "cow", a column containing 
molybdenum 99 which emits a beta particle (an electron) to become the 
"metastable" isotope technetium 99m. This metastable isotope rearranges its 
electrons and emits a gamma particle (photon). This decay event has a half 
life of six hours (2.5 days, or sixty hours, is ten half-lives, which by a 
common convention is the point at which no significant radioactivity 
remains). The decay product, technetium 99, has a half life of six million 
years, so that it emits only a minuscule amount of radiation in the 
foreseeable future.

Bob Richmond
Samurai Pathologist
Knoxville TN

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