biodex ATOMLAB 500, Operation And Service Manual, Page: 206 / 212

Geometry
Geometry Independence means that the indicated activity does not change with volume or
configuration of the source material. The test is performed using a syringe that is normally
used for injections. The following test assumes injections are performed with 3ml plastic
syringes and radio pharmaceutical kits are made in 30 ml glass vials. If they are not used,
change the procedure to ensure that the syringes and vials used are tested throughout the
range of volumes commonly used.
If a significant volume correction results from these procedures, the tests are repeated to
verify. Atomlab dose calibrators are tested for volume dependence in Beta measurements that
are expected to be worst case and the results are 0.13%/ml.
2
Note: There are two methods that can be used to calculate the results:
1. Select a normalized volume and decay-correct the activity readings for the other
volumes to the same time. Divide the calculated activity for each volume by the actual
reading to arrive at the correction factor for each volume.
2. Take the average of all the volume activity readings. Divide the average activity by the
activity of each volume to arrive at the correction factor for each volume. If the test
takes longer than ten minutes, decay-correct the readings.
Example of a Syringe Test:
1. In a small vial, mix 2.0 ml of a solution of Tc-99m with an activity concentration between 1
and 10 mCi/ml.
2. Set out a second small vial containing non-radioactive saline solution.
3. Draw 0.5 ml of the Tc-99m solution into the syringe and assay it.
4. Record the volume and the activity of the first assayed sample (see Figure J.2).
5. Remove the syringe from the calibrator, draw an additional 0.5 ml of non-radioactive saline
into the same syringe (total volume of 1.0 ml) and assay it again. Record the volume and
measured activity on the Geometry Test form.
6. Repeat step 5 twice more until 1.5 ml and 2.0 ml have been assayed and recorded.
7. Assay the vial used to draw the saline into the syringe. If the measured activity is greater
than 1% of the 0.5 ml syringe assay, Tc99-m was lost during filling. Repeat the procedure.
8. Calculate the results using one of the following methods:
•
Select a normalized volume and decay-correct the activity readings for the other
volumes to the same time. Divide the calculated activity for each volume by the actual
reading to obtain the correction factor for each volume.
•
Take the average of all the volume activity readings. Divide the average activity by the
activity of each volume to obtain the correction factor for each volume. If the test takes
longer than ten minutes, decay-correct the readings.
9. If any correction factor is greater than 1.05 or less than 0.95, it is necessary to make a
correction table that allows conversion from
indicated activity to true activity . If necessary,
2
See Accurate Dose Calibrator Activity Measurement of Y-90 Ibitumomab Tiuxetan , J.A. Siegel,
et al., J Nuci Med., 2004, 45:450-454.