Limitations to Allowable Period of Wear - NVLAP Statement

["Sandy Perle" <sandyfl@EARTHLINK.NET>]

The following statement regarding extended dosimetry wear was issued 

to all NVLAP Labortaories on July 12, 2001:



Although NVLAP normally addresses only measurement issues, the

question of what measurements are important, and the impact of

improved measurement capabilities on the ultimate objectives of the

measurements and control often cannot be avoided.  The following

discussion is one of these times; it is intended for NVLAP assessors

and accredited laboratories. Please contact me at the email or snail

mail addresses below for continued dialogue, which I will share with

the dosimetry community. Thank you.



As ionizing radiation dosimeter processing technology has advanced,

fade and background for both film and TLDs can be corrected over

considerably longer periods of time than was considered feasible just

a few years ago. In addition, the last major revision to 10 CFR 20

revised the dose limits from quarterly to annually. The National

Voluntary Laboratory Accreditation Program (NVLAP) has been asked if

there are any limitations to the allowable period of wear for a

dosimeter.



The issue of how long a dosimeter may be worn is both an issue of

technical acceptability and regulatory policy. Although the NVLAP is

not "voluntary" for ionizing dosimeter testing laboratories providing

services to satisfy Nuclear Regulatory Commission (NRC) requirements

in 10 CFR 20, NVLAP is not a regulatory agency. It does, however,

establish technical acceptability of dosimeter processing through its

proficiency testing and on-site assessment programs.



NRC specifies the exchange frequency for personnel dosimeters

processed by an accredited NVLAP processor only in cases where high

doses are more likely to occur (irradiators, well loggers, and

radiographers). That exchange rate is 1 month for film badges and 3

months for TLDs and other dosimeters. NRC does not specify the

dosimeter exchange frequency for other types of licensees. State

regulations should be consulted for the monitoring requirements

pertaining to x-ray equipment or accelerators and to

naturally-occurring or accelerator-produced radioactive materials,

which are outside NRC jurisdiction.



If processors pursue extended wear periods, they should be prepared 

to support the wear period with documentation should litigation 

arise.  



NVLAP requires that a processor establish and document a quality 

system appropriate to the scope of its dosimetry processing 

activities in accordance with the requirements of ISO 17025.  The 

NVLAP General Operations Checklist, which addresses these 

requirements, contains at least two  items relevant to wear periods: 

4.1.2 states "It is the responsibility of the laboratory to carry out 

its testing and calibration activities in such a way as to meet the 

requirements of this handbook and to satisfy the needs of the client, 

the regulatory authorities or organizations providing recognition."  

In this regard processors should communicate with clients about their 

needs and provide advice about the consequences of particular 

dosimeter use or processing practices (such as wear period length) on 

the accuracy of dosimetry measurements.  



5.4.6.1 states that "Testing laboratories shall have and shall apply 

procedures for estimating uncertainty of measurement."  The wear 

period or exchange frequency could be a major component of the 

uncertainty of measurement results. In addition, NVLAP's Specific 

Operations Checklist for dosimetry includes two items that must be 

accommodated: 



5.1(3) "Fading of TLD materials under normal conditions of use, is 

documented and accounted for over the intended period of use...." In 

order to provide good customer service, dosimetry testing facilities 

should collect data over a period of time beyond the intended period 

of use because there will be wearers who turn in their dosimeters 

late. A rule of thumb used by most dosimetry testing labs is to 

characterize the fading characteristics of their TLDs for twice the 

intended wear period.  



8.3 "Protocols for routine processing are defined and can be shown to

be consistent with NVLAP testing procedures." NVLAP proficiency

testing is only over a 1-month period. Results using a proficiency

testing laboratory for the wear/exchange period of interest should be

obtained, and the uncertainties compared with the normal NVLAP

proficiency testing period, to demonstrate this consistency. In

addition, the requirements of the General Operations Checklist,

Section 5.4, Test and calibration methods and method validation, must

be defined and documented in the Quality System to justify any

dosimeter wear period, be it for 1 month or for 1 year.



In our discussions with Health Physicists, however, perhaps the most 

important reasons to approach this issue more conservatively than 

technically feasible are from the health physics and ALARA aspects. 

Radiation exposure (individual radiation exposures as well as 

collective dose equivalent) must be kept As Low As Reasonable 

Achievable (ALARA principle), not at or just below regulatory limits. 

As an example, an extended wear/exchange rate would not be 

appropriate in monitoring pregnant radiation workers to demonstrate 

compliance with both the total dose to unborn baby and rate of 

accumulation requirements. A fetus is limited to 500 mrem/gestation 

period accumulated at a fairly even rate of the course of the 

gestation period. This implies monitoring of pregnant radiation 

workers at an increased frequency (i.e. monthly) in order to be an 

effective radiation protection management tool.  



All of this discussion emphasizes the need for NVLAP accredited labs 

meeting ISO/IEC 17025 to discuss with its client(s) the need for 

data, measurements, etc. to be in place to ensure that the lab has 

the capability of providing the requested services. 

____________________________________________  



Dr. Carroll S. Brickenkamp

National Voluntary Laboratory Accreditation Program

Program Manager, Dosimetry, Construction, Acoustics

National Institute of Standards and Technology

Stop 2140

Gaithersburg, Maryland 20899-2140

U.S.A.

Telephone: 301.975.4291

Fax: 301.926.2884

carroll.brickenkamp@nist.gov



------- End of forwarded message -------



------------------------------------------------------------------------

Sandy Perle					Tel:(714) 545-0100 / (800) 548-5100   				    	

Director, Technical				Extension 2306 				     	

ICN Worldwide Dosimetry Service		Fax:(714) 668-3149 	                   		    

ICN Pharmaceuticals, Inc.			E-Mail: sandyfl@earthlink.net 				                           

ICN Plaza, 3300 Hyland Avenue  		E-Mail: sperle@icnpharm.com          	          

Costa Mesa, CA 92626                    



Personal Website: http://www.geocities.com/scperle

ICN Worldwide Dosimetry Website: http://www.dosimetry.com



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