Re[2]: Thalium Stress Test (fwd)

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

>     An effective halflife estimate of that sort is what they gave one of
>     my co-workers.  It was wrong in practice.  He was 'hot' for well over
>     the 23 days indicated by that thumbrule for a 201 Tl stress test (and
>     far over the week-and-a-half the lab tech told him).  It was more like
>     2-3 months before he was able to pass through a portal monitor without
>     an alarm.
>
>     If there was an isotopic analysis to check for impurities that might
>     have skewed the figures, I never heard about it.
>
>     Dave Neil
>     neildm@inel.gov

I have an old manufacturer's product sheet for Tl-201 radiopharmaceutical.
It quoted an impurity level of <3% Tl-202 [half life 12.23 days, principal
gamma emission 439 keV] at time of calibration. This longer lived impurity
was a determining factor on the expiry time of 120 h after calibration.

Tl-200 and Pb-203 are also possible contaminants of Tl-201, but with
shorter half lives of 26.1h and 52.1 h respectively.

The whole body retention of thallium is said to be a two-exponential
function with half-times of 7 days [63%] and 28 d [37%], so the patient
could set off a sensitive meter some weeks after a stress test if there was
any Tl-202 impurity in the injection.

Jocelyn Towson, RSO

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