Re: In-111 pentetreotide

[michael_coogen@hq2ccgw.hq.dla.mil]

If 10 percent of the initial Indium-111 ( 5mCis) remains in the body after 48 
hours, you will have about 250 uCi remaining.  You must take into account that 
indium-111 has a half life of 2.8 days and has almost decayed through one 
half-life.  If this is not an emergency situation, then I would wait 28 days and
schedule the surgery; that means that 10 half-lives have transpired.  Indium-111
has been used to perform brain scans.  It appears that these physicans are 
neuro-surgeons.  Since indium-111 is commonly used as a diagnostic means, just 
wait until 10 half-lives have expired to perform surgery.  Can't reason why one 
would use a probe to locate brain tumors.  You could administered Indium-111 and
image on a gamma-camera.  If it is an emergency, MRI or CT would produce the 
same information.  Indium-111 usually is administered in a dose of 0.25 to 0.5 
mCis.  Target organ is choriod plexus at 3-6 rads and 0.15 to 0.3 rads whole 
body.  All specimens remove from patients, unless there is no specimen, must be 
evaluated by the Pathology department.  I believe that this is law.  Most 
hospitals use short-lived isotopes and allow 10 half-lives to transpire before 
performing elective surgery.  This reduces the handling of radioactive specimens
by department of pathology....good luck...mike coogen


_____________________________ Reply Separator _________________________________
Subject: In-111 pentetreotide
Author:  radsafe@romulus.ehs.uiuc.edu at hq2ccgw
Date:    9/14/95 11:19 AM


Our Surgery group has purchased some type of probe for use in 
localizing tumors labelled with In-111 pentetreotide (commercially
available radiopharmaceutical).  Of course, they didn't bother to talk with 
us (Radiation Safety) before they decided to pursue this.  Now they
want to know what radiation safety procedures apply (and they want to 
know yesterday - sound familiar).  Based upon info from our nuclear
medicine dept and the package insert for the In-111, it appears that about 
10% of the administered activity (5 mCis) remains in the patient after 48 
hours.  It is difficult to determine what fraction of that remaining activity 
will actually be located in the tumor - it's probably variable, depending 
upon the tumor type and size (my opinion).
     
Assuming all of the residual activity is in the tumor results in a tumor 
activity of about 0.5 mCis.  Using the gamma constant from the package 
insert, this would result in an exposure rate at 1 cm of about 1.61 R/hr 
(obviously somewhat dependent on tumor size, concentration, etc.). 
Using inverse square, the exposure rate at 0.5 M (estimate of whole 
body exposure rate) would be about 0.64 mR/hr.
     
We are attempting to obtain info from the surgeons regarding proximity of 
their hands to the tumor and the length of handling time of the tumor itself. 
We are also attempting to find out where the tumor goes (Pathology?)
after it is removed.  Personnel monitoring (whole body and more 
importantly, ring badges) are being considered; however, they have to 
be sterile and surgeons don't like to be "encumbered" by ring badges. 
One of my staff intends to be present when they first use this thing - that 
will probably provide the best info.
     
Advice from anyone with experience with this procedure would be
appreciated.  I'm sure I left out some important detail - if so let me know.  I 
will also share our experiences with this as they unfold.
     
Usual disclaimers apply.
     
Mack R.