Re: Sewer Releases: Nuclear Medicine Patients

[HAENCHEN@SLUVCA.SLU.EDU]

As others have commented, we do not track patient releases for the obvious
reasons, e.g. tracking in-house patients vs. outpatient
 exams vs. outpatient exams, etc.
If your looking for some rough but significant patient releases, consider
therapeutic administrations of I-131.  Doses in excess of 30 mCi require 
confinement of the patient to a private room per 10 CFR 35.75.  Doses at
our institution are typically 150 mCi, and the patient is hospitalized
for about 48 hours.  The administrations occur after most of the thyroid 
tissue has been surgically removed.  I am told by our Nuc. Med. physician
that typical uptake under these conditions is on the order of 2 to 4 %.
The majority of the remaining 96 to 98 % will be excreted within the first 
24 hours.  A rough estimate (based upon exposure rate measurements 
immediately after administration and at 24 hours @ 1 meter from the patient)
is that this may be 60 or 70 % excretion during 1st 24 hours.  Thus, we 
may have 90 to 100 or more mCi of I-131 flushing down the toilet in a 
single day.
We may have about 10 such patients per year.  Where I worked previously, 
we averaged 30 to 40 patents per year, and at times had two or three patients
being administered on the same day.  I know of other facilities that may
have higher numbers of such patients per year.  Obviously, research related
sewer disposals can be insignificant when compared to patient excreta.

Also of note to others pursuing sewer discharges with the local sewer 
authority:  In St. Louis, the Metropolitan Sewer Distric of St. Louis has
limited the aggregate of all discharges to a given treatment facility to
1 Ci per year.  This means that not only are the NRC limits of 5 Ci H-3,
1 Ci C-14, and 1 Ci aggregate of all other radionuclides out the window,
but we must "share" the 1 Ci limit for a given treatment facility with
other licensees whose sewers discharge to the same treatment facility.
The Metropolitan Sewer District of St. Louis takes this into account when
issuing their approval and restrictions.  The ordinance defining this limit
has been in effect since August of 1991.  Incidently, the ordinance does
exempt patient excreta, consistent with NRC.

Good Luck with your pursuit!

Mark Haenchen
Saint Louis University