[ RadSafe ] Linearity with Tc99m shortage?

[Daniel Kane]

Both Tl-201 and Tc-99m labeled compounds are used for the determination of
myocardial perfusion which is a measure of coronary artery disease. Both
agents have their pluses and minuses in my U.S. based (diagnostic nuclear
medicine) consulting practice both are used but Tc-99m labeled agents are
favored.

To determine which agent is used the clinician takes into consideration the
size of the patient, the suspected disease state, the equipment available,
and probably a host of other points that they do not discuss with me. 

In the U.S., I would guess that because of the higher energy of Tc-99m along
with the shorter T1/2 (allowing a higher MBq dosage) Tc-99m labeled agents
have the greater favor. Tl-201 and the Tc-99m labeled agents have slightly
different kinetics and extraction fractions and this too if factored into
the clinical decision as to what agent to use when. The 3 day T1/2 half of
Tl-201 limits the MBq that can be used and the lower ~70 keV photon has a
lower resolution in clinical imaging.

Dan Kane
Associates in Medical Physics, LLC
www.medphysics.com
dankane at mindspring.com

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf
Of Franz Schönhofer
Sent: Friday, December 07, 2007 11:47 AM
To: 'Brunkow, Ward'; 'Diane Griffiths'; radsafe at radlab.nl
Subject: AW: [ RadSafe ] Linearity with Tc99m shortage?

Ward,

There are typing errors in (both) your messages: Thallium has the chemical
symbol "Tl" and the isotoped used in cardiac medicine is Tl-201. "Tc-99" is
never used, not only because it is a pure beta emitter which cannot be used
for szintigraphy, but also because of its long half-life (211 100 years) and
therefore very low specific activity. What is used is the metastable Tc-99m
as a pure gamma-emitter and with a short half life of 6 hours, which is very
favourable with regard to patient radiation protection considerations. 

Interesting to read that one can use either radionuclide - I had the
impression that they are used according to different diagnostic tasks. I
remember that after my coronary infarction I underwent two tests with both
Tl-201 and Tc-99m. Maybe somebody on RADSAFE can explain this?

Best regards,

Franz

Franz Schoenhofer, PhD
MinRat i.R.
Habicherg. 31/7
A-1160 Wien/Vienna
AUSTRIA


-----Ursprüngliche Nachricht-----
Von: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] Im Auftrag
von Brunkow, Ward
Gesendet: Freitag, 07. Dezember 2007 15:05
An: Diane Griffiths; radsafe at radlab.nl
Betreff: RE: [ RadSafe ] Linearity with Tc99m shortage?

It is my understanding that most medical facilities use Thallium anyway
over TC99 for Cardiac stress tests, it is much cheaper but has much
longer T 1/2. The last time I had the procedure I requested Tc99 as I
didn't want the longer T1/2 while working in a highly restricted nuclear
facility, and they accommodated me, who know what they charged the
insurance company.  

Ward

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Diane Griffiths
Sent: Friday, December 07, 2007 4:28 AM
To: radsafe at radlab.nl
Subject: [ RadSafe ] Linearity with Tc99m shortage?

I know we have discussed that hospitals can't get the Tc99m for patient 
studies, this brings me to another question.. How can we do linearity on
the 
Dose Calibrators?

I have two locations where the linearity is due by the end of this
month, 
and they can't get any Tc99m at all. They have switched their cardiac 
procedures to Thallium until the shortage is over.

Diane

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