Radiopharmaceutical patient release

[ASOLUTION8@aol.com]

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:

"Did I sleep through a change in 20.2101(a) which requires that records be
kept in units of curies, rads, and rems?  If not, why is this rule written in
terms of sieverts?  I think that requiring one set of units while the
regulations are written in a separate set of units is a mistake."

Reply: The rule actually is written in terms of both the traditional units of
rems as well as the SI units of sieverts.  My understanding is that this is
being done on all new regulations and guides to facilitate a transition to
the SI units sometime in the indefinite future.

"In response to a comment that the dose-based release limit will necessitate
that many personal questions will need to be asked, the NRC says, "nearly all
patients will be released based on default assumptions which do not require
any personal information from the patient."  But in response to a subsequent
comment, the NRC says, "In special situations, such as when a released
patient would immediately board an airplane and would therefore be in close
contact with one or more individuals, it may be necessary to base the release
criteria on a more realistic case-specific calculation.  So, how does one
determine if a "special situation" exists if one does not ask personal
questions?  Or should we follow a "don't ask, don't tell" philosophy?"

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.  

I don't think this is unreasonable.  Would you want to sit right next to
someone (on a bus, subway, airplane, movie theater, concert, etc.) who
received 150 mCi of iodine-131 a few hours earlier?  After all, the average
spacing of airplane passengers is a little closer than the 1 meter assumed in
the calculation, and the r squared factor can really up the dose.  

It will be very interesting to see what the final versions of those documents
(including the Regulatory Guide) say on this issue, but those documents have
not yet been issued.  

And, by the way, a little self-promotion.  My company is developing software
to implement the rule.  It will do the necessary calculations to allow
earlier release of some therapy patients, maintain the necessary records, and
automatically print the required instructions.  Of course, we can't finish it
until the NRC releases its final documents.  If you would like information on
the software when it is completed, please e-mail me at the e-mail address
below.  (If you've already asked for info, no need to request it again.  I'll
send the info as soon as the NRC releases the necessary implementation
documents.)

Michael McGuire
Simplified Solutions Software, Inc.
1466 Chapin Street NW, Suite 1
Washington, DC 20009
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