Re: 2 mr in 1 hour limit

[carol marcus <csmarcus@ucla.edu>]

At 08:57 AM 7/7/99 -0500, you wrote:
>Dear Radsafers:
>
>Carol Marcus indicated that the 2 mrem in any on hour limit was changed to
>500 mrem to individuals exposed to patients who had received radioactivity
>for medical purposes.  Unless another change that I am not aware of has
>occurred, I don't believe Carol's statement is entirely correct.  10 CFR
>35.75(a) does allow hospitals to release patients if it can be reasonably
>assured that members of the public will not receive greater than 500 mrem
>from those patients.  However, it is my understanding that if the patient is
>hospitalized for radiation safety purposes (e.g., the 500 mrem limit cannot
>be assured), the licensee is required to meet the requirements of 10 CFR
>20.1301(a)(1) - 100 mrem to a member of the public in one year and 10 CFR
>20.13019(a)(2) - 2 mrem in any one hour limit in an unrestricted area.  Both
>of those sections provide relief from the requirements if a patient has been
>released under 10 CFR 35.75(a).  On the other hand, if the patient has not
>been released under that section, I believe the part 20 limits continue to
>apply.  Carol's interpretation would save us a lot of grief, but I don't
>think we can apply that interpretation for patients who are hospitalized for
>radiation safety purposes (e.g., temporary brachytherapy).  
>
>As an aside, the "100 mrem in a year" limit applies to an individual while
>with the "2 mrem in any one hour" limit applies to an unrestricted area
>rather than an individual.  While the two limits may appear to be similar,
>one can assign an occupancy factor to the 100 mrem individual limit, but not
>to the 2 mrem in an hour limit.  
>
>To illustrate this, let me cite an example.  Suppose one measures an
>exposure rate outside a  brachytherapy patient's room door (i.e., the
>boundary of the restricted area) of 3 mR/h (assumed to be 3 mrem/h).  If the
>total treatment time for that patient is 45 hours, the integrated dose
>equivalent outside the door would be 135 mrem.  Assuming a very conservative
>occupancy factor of 0.25 (i.e., someone stands outside the door 25% of the
>time), the integrated dose equivalent to such an individual would be 135
>mrem x 0.25 or 34 mrem.  That obviously meets the "100 mrem limit to an
>individual" requirement.  Unfortunately, the 3 mrem exposure rate outside
>the door exceeds the "2 mrem in any one hour limit to an unrestricted area"
>requirement; therefore, some type of precautions must be implemented to meet
>that requirement.  That has never made much sense to me, but who said
>regulations are always logical.
>
>Regards,
>Mack R.  
>
>Mack L. Richard, M.S., C.H.P.
>Radiation Safety Officer - IUPUI/Indiana Univ. Med. Cntr.
>Phone #: (317) 274-0330   Fax #: (317) 274-2332
>E-Mail Address:  mrichar@iupui.edu
>
>************************************************************************
>The RADSAFE Frequently Asked Questions list, archives and subscription
>information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
>Dear All:

The question originally was for I-131, where virtually all patients, even if
they are hospitalized, can be "released in accordance with 35.75".  They may
be hospitalized for other reasons (concern about possible arrhythmias,
etc.).  If the patient CANNOT be released because he really could reasonably
give someone over 500mrem, then the Part 20 limit still applies. 

Ciao, Carol

<csmarcus@ucla.edu>

************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html