Download Precise 82 Rb Infusion System For Cardiac Perfusion Measurement

82
Rb Elution System Control
Ran Klein, University of Ottawa
Breakthrough Sr Activity
Elution of 82Sr and
85
Sr isotopes (half-life of 25 and 65 days respectively) to the
patient is undesired, as Sr tends to accumulate in the bone marrow, which is particularly
radiation sensitive [15]. Of concern to us was premature Sr breakthrough, due to the
pulsating flow of saline through the generator as the valve is cycled.
Daily calibration samples are used to test for the breakthrough of Sr activity; if
significant Sr activity is detected, the generator cannot be used on humans. The
specifications of our generator permit 20 L of saline to be eluted before Sr breakthrough
should be experienced. We continued to use the generator on the development system past
the specifications and experienced first breakthrough after approximately 40 L were eluted
through the generator. Once breakthrough appeared, it was tracked over two months. The
measured breakthrough activity reached a maximum around the 40th day. However, if the
activity is corrected for
82
Sr decay it becomes clear that the breakthrough (82Sr to
82
Rb
activity ratio) continues to increase as shown in Figure 5-15.
Sr/82Rb
activity ratio
0.025
82
82
Sr Breakthrough
0.02
0.015
0.01
0.005
0
90
80
70
60
50
40
30
20
10
0
Day
Figure 5-15 - Breakthrough ratio progression over time as measured and corrected for 82Sr decay.
We have no data to suggest premature breakthrough due to the cycling valve.
However, testing on additional generators is required to determine whether breakthrough is
accelerated or not. Sr breakthrough does not appear to be a safety concern as it changes
slowly and is tested for on a daily basis as part of the daily protocol.
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