[Intl_DxMedPhys] Extravasation dose estimate

[Adam Springer]

I was asked to estimate the skin dose from an 18F extravasation. I'm sure
it won't be the last request, so I'm trying to figure out a procedure. The
total activity measured in a test syringe images is 35% less than the
actual activity. I'm not sure how accurate this measurement should be and
would appreciate any expert guidance.

I plan to measure the total extravasated activity from the patient images
to enter into the University of Texas (UT) Radiopharmaceutical Infiltration
Dosimetry Estimate (RIDE) <https://urldefense.com/v3/__https://gsm.utmck.edu/research/MITRP/RIDE.cfm__;!!KGKeukY!1HslGXroK0I59G3ELoPBWs_YPsCABLNSpFxijIaXWrVSZeKDG1oPLruW694Q5IMWtQ2oejbOI757ItX-nUU3rczSG3ad6RcgbKAOUg$ >
Tool. To verify my method for measuring total activity, I tested the
process on images of a syringe with known activity.

The test syringe (9.07-mCi at start time) was scanned with a single
2-minute bed on a Canon Cartesion Prime. Reconstruction was done with PSF,
TOF 3D OSEM. The images were corrected for decay (start time), randoms
(delayed), attenuation (CT), and scatter (MISE). I'm using ImageJ to open
the DICOM images. I used Z-Project... to *sum* all of the images then
multiplied the mean of the summed image by the total volume to get  5.9
mCi.

I expect individual pixels to be underestimated due to the partial volume
effect, but I assume the total activity should be immune to that. Is my
assumption wrong? Can one of the corrections be inappropriate (scatter or
randoms?) for such a small, concentrated source? Or is a 35% underestimate
within the expected range for total activity? Or is it likely an error in
my calculations?

If anyone on the list has experience making these measurements from DICOM
images, would you be willing to share some tips or help me understand what
I'm missing? If anyone responds directly, I'll gladly follow up with the
list when we have a final answer.

Thanks in advance!
Adam

===============================================
Adam C. Springer, MS, DABR®
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