RE: Bone Scan

[Karin Gordon <KGordon@exchange.hsc.mb.ca>]

Hi 

Technetium-99m (Tc-99m) is the radioactive label on the radiopharmaceutical
he will be recieving.  It is a pure gamma emitter (140 KeV) with a half-life
of 6 hours.  The radioactive pharmaceutical  is excreted rapidly and
primarily via the kidneys in urine, although all body fluids (sweat, saliva,
tears, etc.) will be temporarily radioactive.  The biological half-life is
highly dependent on  patient pathology, radiopharmaceutical uptake,
hydration and excretory renal function, and  typically demonstrates a
tri-exponential pattern.  Therefore the effective half-life (and resultant
dose rate external to the patient) is variable.  Castronovo has looked at a
number of exposure scenarios (1) and for example calculated  that a bone
scan patient with bony metastases (greater radiopharmacetical uptake)
injected with 20 mCi Tc-99m and sitting at a table with a relative at a
distance of 3 feet for the first two hours post injection would give an
external radiation dose of 3 mrem to that individual. Obviously close
contact (holding an infant) for extended periods soon after the injection
can give a more significant dose to the child.  There are some pretty good
(and free) software programs available for calculating dose to caregivers
and family based on contact times and distances (2).  

Generally to minimize external radiation dose to others we advise the
patient not to have close and extended contact with children and pregnant
people for 24 hours after the radiopharmaceutical injection. If at all
possible, have another adult be the child's primary caregiver for  the child
for the first day. This doesn't mean the patient can't pick up a baby
briefly, change a diaper, etc. ride in the same vehicle, etc.  The point is
to avoid close contact with the child for long periods during the first day.
When I was a young Mom with a fussy baby (survived 3!!), I used to pop the
infant into a cloth harness stapped onto my torso, and carry that baby
around all day while doing housework, cooking, etc. Also often bought the
baby into bed at night.  Soothing for the babe, and also for the Mom, as I
remember. But definitely what I would NOT recommend for the first 24 hours
after a bone scan injection. 

Conscientious handwashing after using the toilet or before any food
preparation will prevent the spread of trace radioactive contamination to
family members.

(1)Frank Castronovo.  A Mathematical Method for Determining Radiation
Exposures Surrounding Technetium-99m-MDP Patients.  Journal of Nuclear
Medicine Techology Vol. 21, No. 4, pp 224-230 Dec. 1993
(2) Cormack J. and Shearer J. Calculation of Radiation Exposure from
Patients to whom Radioactive Materials have been Administered.  Phys. Med.
Biol 43 99. 501-506 (1998) 

-----Original Message-----
From: Mark Settles [mailto:msettles@cswnet.com]
Sent: Wednesday, April 12, 2000 12:53 PM
To: Multiple recipients of list
Subject: Bone Scan


I am looking for information for a friend.  He is having a Bone Scan in
which he will have 21 millicuries of Tc99 injected into his system.  The
question is;  Are there any concerns he should have or precautions he should
take with body fluids, perspiration, etc.  He does have a 2 month baby in
the home.   What dose rates will he see contact with his body and where will
be the most concentration?  How long should his body take to rid itself of
all activity?

Thanks in advance.  You may reply to me personally at

msettles@cswnet.com

Thank you.



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