Re: Prenatal Exposure Limit

[sandy_perle@email.fpl.com]

     Bob is absolutely correct. The following is the actual rule:
     
      20.1208  Dose to an embryo/fetus.
     
        (a) The licensee shall ensure that the dose to an embryo/fetus 
     during the entire pregnancy, due to occupational exposure of a 
     declared pregnant woman, does not exceed 0.5 rem (5 mSv).  (For 
     recordkeeping requirements, see  20.2106.)
     
        (b) The licensee shall make efforts to avoid substantial variation 
     above a uniform monthly exposure rate to a declared pregnant woman so 
     as to satisfy the limit in paragraph (a) of this section.
     
        (c) The dose to an embryo/fetus shall be taken as the sum of--
        (1) The deep-dose equivalent to the declared pregnant woman; and 
        (2) The dose to the embryo/fetus from radionuclides in the 
     embryo/fetus and radionuclides in the declared pregnant woman.
     
        (d) If the dose to the embryo/fetus is found to have exceeded 0.5 
     rem (5 mSv), or is within 0.05 rem (0.5 mSv) of this dose, by the time 
     the woman declares the pregnancy to the licensee, the licensee shall 
     be deemed to be in compliance with paragraph (a) of this section if 
     the additional dose to the embryo/fetus does not exceed 0.05 rem (0.5 
     mSv) during the remainder of the pregnancy.
     
      20.1502  Conditions requiring individual monitoring of external and 
     internal occupational dose.
     
        Each licensee shall monitor exposures to radiation and radioactive 
     material at levels sufficient to demonstrate compliance with the 
     occupational dose limits of this part.  As a minimum--
     
        (a) (2) Minors and declared pregnant women likely to receive, in 1 
     year from sources external to the body, a dose in excess of 10 percent 
     of any of the applicable limits in  20.1207 or 20.1208, and
     
     (b) Each licensee shall monitor (see  20.1204) the occupational 
     intake
     of radioactive material by and assess the committed effective dose 
     equivalent to--
        (1) Adults likely to receive, in 1 year, an intake in excess of 10 
     percent of the applicable ALI(s) in Table 1, Columns 1 and 2, of 
     Appendix B to  20.1001 - 20.2401; and
        (2) Minors and declared pregnant women likely to receive, in 1 
     year, a committed effective dose equivalent in excess of 0.05 rem (0.5 
     mSv).
     
     
      20.2203  Reports of exposures, radiation levels, and concentrations 
     of radioactive material exceeding the limits.
     
        (a) Reportable events.  In addition to the notification required by 
      20.2202, each licensee shall submit a written report within 30 days 
     after learning of any of the following occurrences:
        (1) Any incident for which notification is required by  20.2202; 
     or 
        (2) Doses in excess of any of the following: 
        
        (iii) The limits for an embryo/fetus of a declared pregnant woman 
     in  20.1208; or
     
     
     
     Sandy Perle
     Supervisor Health Physics
     Florida Power and Light Company
     Nuclear Division
     
     (407) 694-4219 Office
     (407) 694-3706 Fax
     
     sandy_perle@email.fpl.com




______________________________ Reply Separator _________________________________
Subject: Prenatal Exposure Limit
Author:  radsafe@romulus.ehs.uiuc.edu at Internet-Mail
Date:    10/20/95 10:12 AM


I'd like to point out that there has been some misuse of the concept of the
prenatal exposure limit in this forum recently. The dose limit in the
regulations (DOE and NRC) applies to the fetus, not the mother. The
regulators conveniently allow us dosimetrists to use the external deep dose
equivalent to the mother as a fair estimate of the external deep dose
equivalent to the fetus. Since most dose arises from external exposure, this
leads to a tendency to see the mother's dose and the fetal dose as the same
thing. However, when the exposure involves internal radioactivity (as in
P-32 at the NIH), the accepted practice is to either calculate the true
fetal dose, a feat destined to cause either lasting fame or insanity, or use
the committed dose equivalent to the mother's uterus (adjusted to the
gestation period) as the fair estimate of the fetal dose. In such a case, an
intake just under that allowed for *occupational* exposure of the mother
(and resulting in 4.8 CEDE) will have much more important dose implications
for the fetus, since the dose limit is an order of magnitude lower and the
dose quantity of interest is no longer CEDE but CDE to the uterus.
Bob Flood
Unless otherwise noted, all opinions are mine alone.
(415) 926-3793
bflood@slac.stanford.edu