Radiation Limits / Categories for NM and RadTherapy Techs

[Chris Davey <cdavey@med.phys.ualberta.ca>]

Background:
At the Cross Cancer Institute, we find that our Radiation Therapists (the
techs who operate the linear accelerators, cobalt machine, etc.) rarely
get enough exposure in each quarter to register on their TLDs (we use
Landauer, so the minimum detectable is 10 mrem / 0.1 mSv).  We conclude
that their annual exposure is around 30 to 50 mrem / 0.3 to 0.5 mSv.  In
the Canadian regulations, (Atomic Energy Control Regs) the definition of
an Atomic Radiation Worker is "any person who is likely to receive a dose
... in excess... [of 0.5 rem / 5 mSv]"

Therefore, our therapists are _not_ designated ARWs, but remain under the 
public limits.

Our NM techs used to get about 190 mrem / 1.9 mSv per annum whole body,
which might seem a similar situation , but it looks like their increasing
workload (we do a lot of I-131 therapies and have had staff cuts) may
raise this to 250 mrem / 2.5 mSv.  What may put them into the ARW
category, however, is that they may be nearing the extremity dose limits
(public limits are 7.5 rem / 75 mSv).  Canadian regulations only require
ring TLDs to be worn in the case of certain isotopes - I-131 is not one of
these.  Despite this, we do provide ring TLDs to our NM techs, but because
they are not required to wear them at all times, it has been the norm that
few techs actually wear the ring TLD 'religiously'.  (This should explain
the uncertainty about approaching the extremity dose limit.)

I have several questions relating to this (mainly for Cancer Hospitals):

1	what are the typical annual doses that your NM techs and Radiation
	Therapists get?

2	have any other clinics / hospitals designated their techs as ARWs
	(or the equivalent in your country), even though their exposures
	are not at all likely to exceed the public limits?

3	how have other facilities handled the extremity dose question
	i.e. where ring TLDs are _not_ required, but the RSO has 'an idea'
	that the extremity dose may be being approached or exceeded?

4	Do other countries have similar rules about extremity monitoring?
	(AECRegs require ring dosimeters when 'handling a container with
	more than 50 MBq / 1.35 mCi of P-32, Sr-89, Y-90, Sm-153 or
	Re-186').


Thanks for your feedback,

Chris Davey

 RSO / LSO  Cross Cancer Institute  11560 University Avenue
 Edmonton   Alberta   Canada  T6G 1Z2
 (780)  432-8616   fax 432-8615
 email: cdavey@med.phys.ualberta.ca
 pager number 005, just call (780)  432-8771 and ask for that pager



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