Answer to Question #10019 Submitted to "Ask the Experts"
The following question was answered by an expert in the appropriate field:
We have a radiation worker who is approaching 50 mSv for the year and I was told by the state that we could apply a Webster's Dose Weighting Factor (I was told to use 0.3) to his exposure because he wears his dosimeter outside the lead apron, by the collar, which is not an accurate representation of his true whole-body dose. Can you give me some information on this topic?
We believe the Webster equation refers to a proposed dose equivalent determination when two dosimeters are worn, one worn at the collar outside a lead apron and one worn at the waist below the apron. E.W. Webster published the equation in the April 1989 Health Physics Journal (56: 568-569) as HE being approximately equal to 1.5 H1 + 0.04 H2, where H1 is a dosimeter under the apron and H2 is the neck dosimeter above the apron. We advise that you should refer back to the individual state regulations to see what may be applicable to your facility.
The section that would be pertinent to the question is Suggested State Regulations, Sec. D. 1201 - Occupational Dose Limits for Adults:
c. ii. When a protective apron is worn while working with medical fluoroscopic equipment and monitoring is conducted as specified in D.1502a.v., the effective dose equivalent for external radiation shall be determined as follows:
(1) When only one individual monitoring device is used and it is located at the neck (collar) outside the protective apron, the reported deep dose equivalent shall be the effective dose equivalent for external radiation; or
(2) When only one individual monitoring device is used and it is located at the neck (collar) outside the protective apron, and the reported dose exceeds 25 percent of the limit specified in D.1201a., the reported deep dose equivalent value multiplied by 0.3 shall be the effective dose equivalent for external radiation; or
(3) When individual monitoring devices are worn, both under the protective apron at the waist and outside the protective apron at the neck, the effective dose equivalent for external radiation shall be assigned the value of the sum of the deep dose equivalent reported for the individual monitoring device located at the waist under the protective apron multiplied by 1.5 and the deep dose equivalent reported for the individual monitoring device located at the neck outside the protective apron multiplied by 0.04.
Nuclear Regulatory Commission Regulatory Issue Summary 2002-06, dated 16 April 2002, also provides an appendix with the above Suggested State Regulations excerpt, along with other references to National Council on Radiation Protection and Measurements Report 122 and American National Standards Institute/Health Physics Society N13.41 on acceptable alternatives for compliance with 10 CFR Part 20 requirements when protective apparel is used. Reference to a 0.3 correction factor can be found in the following documents:
- Suggested State Regulations, Sec. D, 1201, Occupational Dose Limits for Adults.
- NRC Regulatory Guide 8.40 "Methods for Measuring Effective Dose Equivalent from External Exposure," dated July 2010.
- August 2000 Operational Radiation Safety (79 [2 Suppl]: S17-19).
Joe DeCicco, CHP
Cynthia Jones, PhD