Re: Doses in PET centers

[jtowson@nucmed.rpa.cs.nsw.gov.au (Jocelyn Towson)]

>This is a question for that subset of Radsafers who work in or around
>PET centers which have their own cyclotrons.

You might also try pet_mail-request@ncbapsun2.pet.wfu.edu

Looks like no-one else is responding so I might as well plunge in! We have
a 4 year old Siemens CTI scanner, and a PET production laboratory 400
metres away in the on-site National Medical Cyclotron. Our PET exposures
are a matter of continuous determined effort, but stubbornly resist
attempts to bring them into line with those of nuclear medicine staff.

>1.  No. of PET personnel.
All staff are full-time dedicated PET employees.  Significant TLD badge readings
are seen for the clinical registrar, the 3 PET techs and the 2 radiochemists.

>2.  Approximate total mCi of PET compounds handled per month (or week
>or day if that is simpler).

PET production is 4 days/week, Mondays being reserved for cyclotron/PET
chemistry maintenance.  FDG is delivered daily via a pneumatic transfer
system, about 18 GBq at 10 am.  N13 ammonia is delivered the same way
approximately once a week, decayed to about 2 GBq before it is 'handled' by
the PET techs. (Research use of H2O15 for brain activation studies is
included in the dose below for the chemists, but not for the techs and
registrar)

>2.  Range of "whole body" and finger doses among personnel during a
>typical month.
Whole body and finger TLD's are changed 4-weekly.  The average wb badge
readings  [microsieverts/4wks] are registrar 280, techs 470 each, chemists
360 each.

>3.  Highest doses recorded, and explanation for same.
For whole body readings;
Registrar dose range 220-360/4 wks
Tech dose range 130-1100 / 4 wks
Chemist dose range 160-740 / 4 wks
High doses were due to [a] new staff at beginning of learning curve, [b]
one staff member on leave and others in the group taking up the additional
work load
[c] for chemists, occasional targetry problems to fix.
Finger badges averaged 6700/4 wks for the techs, about 450/4 wks for the
registrar.  [Data a bit dodgy because of lost badges, different wearing
positions etc.]

>4.  Your ALARA trigger levels for dose (quarterly or whatever) for
>PET personnel, and how often they are exceeded.

We aim for dose constraint of 5 mSv/y ie 400 microsieverts/badge change.
Not exceeded by registrar, exceeded 22/33 badge changes by techs, 9/22 by
chemists

>As you may have guessed by now, personnel in our PET facility keep
>registering pretty high readings, and I would like to know how they
>compare with other similar facilities.

The doses above should be seen in context of our workload.  This is now
about 6-7 patients per day, ie about 100-110 patients per badge change.
Approx 3/7 neuro cases, 4/7 whole body oncology.  Hearts maybe once a week.
Average patient gets 450-500 MBq of FDG. All doses are drawn up into
perspex shielded syringe and calibrated  [behind oodles of lead] and placed
in mobile lead shield.  Neuro doses are administered via infusion line in
lead pig. Neuro patients all have arteriovenous shunted blood samples, 20
samples over 0-95 minutes post inj, thermoplastic masks fitted when
positioned in camera.   WB doses are injected via bung on three way
tap/cannula. Whole body patients have bladder catheterisation.
Use of electronic personal dosimeters shows that most of the techs'
exposure is from the patient - dose administrations, patient positioning,
blood sampling - and they use every reasonable means they can think of to
minimise time and maximise distance.

I would also be interested to hear how other centres fare, and grateful for
any hints on further dose reductions.

Jocelyn Towson
Radiation Safety Officer
Royal Prince Alfred Hospital
jtowson@nucmed.rpa.cs.nsw.gov.au

>P. Sridhar Rao, Radiology, CWRU / Univ Hosp of Cleveland, Cleveland, Ohio.
>Tel: 216-844-1295.    Fax: 216-844-3300.    E-mail: psr@po.cwru.edu