Re: Radiopharmaceutical patient release

[Darryl Kaurin <kaurin@mail.sep.bnl.gov>]

With regard to public occupancy factors for patients receiving radioactive
material:

At 10:04 PM 2/4/97 -0600, you wrote:
>On January 30, Kent Lambert wrote concerning the NRC's final rule on the
>release of patients administered radioactive materials that was published on
>January 29, 1997:

snip
>
>Reply: The answer to this question seems to be contained in two preliminary
>draft documents that the NRC released to its public document room in
>November.  The doses predicted by an equation that uses a default occupancy
>factor of 0.25 at one meter AND the PHYSICAL half-life of iodine-131 is
>justified by comparison with measured results, which show that the doses
>predicted by the equation are usually (but not always) conservative.  But no
>justification is provided for using an occupancy factor of 0.25 with anything
>other than the physical half-life.  To the contrary, an occupancy factor of 1
>is used when it cannot be assumed that the dose will be incurred over a long
>period of time measured in days.  Thus, the message is that you can use the
>default values based on 0.25 and physical half-life without asking any
>questions, but if you want to take credit for biological excretion AND use an
>occupancy factor of 0.25, you will have to ask a few questions to make sure
>that the occupancy factor of 0.25 is justified.  


We actually calculated public occupancy factors, which we called exposure
factors, based on several published studies carried out in the 1970s which
measured the dose to family members of patients administered I-131 for
thyroid treatment (Kaurin et al. 1996).  One of the studies gave the family
members dosimeters to wear at waist level, and the other study used
dosimeters on the wrist.  For an assumed whole-body effective half-life of 1
day (based on another study), the exposure factor was 0.20 +/- 0.25 for 30
family members.  For an assumed whole-body effective half-life of 8 days
(approximately the physical half-life of I-131), the exposure factor was
0.040 +/- 0.041.  These values excluded the family member with the highest
exposure factor of 22 and 2.8 for the 1 and 8 day assumed whole-body
effective half-life, respectively.  This latter family member took a 2 week
vacation with the patient in a car immediately after the treatment.
Additional details/assumptions can be found in the reference.

Reference

Kaurin, D.G.L, D.E. Barber, A.L. Carsten, J.W. Baum. "Whole-body Effective
Half-lives for Radiolabeled Antibodies and Related Issues", NUREG/CR-6374,
U.S. Nuclear Regulatory Commission, Washington D.C. 1996.

Darryl Kaurin, Ph.D.
Brookhaven National Laboratory
Safety and Environmental Protection Division
Building 535A
Upton, NY 11973-5000
(516)344-3166
kaurin@mail.sep.bnl.gov