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Dose rates from thallium patient
>> NUREG/CR-6345, Radiation Dose Estimates for Radiopharmaceuticals, by
>> the estimable Mike Stabin et alia, gives a patient EDE estimate of
>> 6.0E-1 rem/mCi for thallium-201 chloride (plus contaminants)
>
>How does this relate to 4.7 rem/Ci-hr at 1 cm ?
>(And I'm more curious about the actual whole body dose rather than the EDE
>artifact.)
I think the value of 4.7 rem/mCi-hr @ 1cm from a 1 mCi point source of
Tl-201 may be out of line, maybe by a factor of 10. The air kerma rate
constant for Tl-201 is given as 10.2 microgray/h @ 1 m from 1 GBq
(Groenewald & Wasserman, Hlth Phys 58:655-658, 1990, and same authors in
Eur J Nucl Med 14:569-571, 1988). The equivalent dose rate in skin (air
kerma x 1.1) would be a bit higher, about 11.3 microsieverts/h. This is
equivalent to 0.42 rem/h @ 1 cm from 1 mCi Tl-201.
However this exercise highlights a problem I have with equivalent dose rate
constants (at least those which are used in nuclear medicine). There are
substantial discrepancies between the values in the papers I have quoted
above, and those in the Health Physics and Radiological Health Handbook
(2nd edition). The Handbook values are substantially higher, eg 23.7
microsieverts/h compared to 11.3 for Tl-201, and 33.2 compared to 15.7 for
Tc-99m. I can't see that The Handbook method of calculation which includes
photons down to 10 keV instead of 20 keV would double the dose rate. Can
anyone please shed some light on this?
A VERY rough estimate of whole body dose to a person near a thallium
patient might be obtained by multiplying the dose rate, preferably measured
with an ion chamber, by a factor of 0.6 (males) or 0.4 (females), the
scaling factors which a TLD agency here uses to convert skin dose to
effective dose for exposure to 75-130 kV x-rays.
Jocelyn Towson
Jocelyn Towson, RSO
Dept of PET & Nuclear Medicine
Royal Prince Alfred Hospital
Camperdown, NSW 2050
Australia
tel [national] 02 9515 8011 [international] 61 2 9515 8011
fax [national] 02 9515 6381 [international] 61 2 9515 6381
email jtowson@nucmed.rpa.cs.nsw.gov.au