Scan question: "without definite CT correlate"

[lokibear0803]

I recently received an 18F-DCFPyL scan at a Stanford trial. To summarize the report, a low-dose CT was done for calibration/correction/etc, before the actual DCF scan was done (I'm assuming). This sounds like a standard piece that precedes scans like this.

The report came back with a bit of uptake in one lymph node and maybe 4 foci in seminal vesicle; no bone mets; and this:

"New PyL uptake in hepatic segment 4A/b lesion without definite CT correlate"

...with the Impression describing it as "concerning for hepatic metastasis".

Can someone offer insight in particular on the lack of a CT correlate?

-- why might this kind of thing happen?

-- does it suggest anything at all (other than need for followup, which I'm doing)?

-- is there a way these types of things typically play out ... in particular, in the liver ... e.g. is it "likely" a false positive?

-- is it just a result of low-dose CT (such that now I need the real deal CT or MRI)?

If this is typically about the low-dose calibration CT, it makes me wonder why the other foci didn't have the same thing, since they were quite small (4-7mm). Does it mean the liver spot was even smaller than that? Seems like in that case, none of what was seen here would show up on a standard CT or MRI, am I right? Likely I'm conflating some things here based on my ignorance.

Any thoughts at all to fill the vacuum are appreciated, while I wait for the next radiologist to offer an interpretation. Hopefully your thoughts will help guide my followup questions once that's done.

Thanks very much in advance.

[GP24]

The 18F-DCFPyL scan is a 18F-DCFPyL PET/CT. So they have CT images available. They will see whether what is indicated by the PET image has a correlate on the CT. If the detected lesion is too small to look suspicios on the CT the report may mention: there is no correlate on the CT image.

[lokibear0803 in reply to GP24]

Yeah, I guess that goes to my sidebar question - wouldn't ALL of these mets be too small to be seen on a CT (and thus, they would all have no definite CT correlate)? The range of sizes given were 4mm-7mm.

[GP24 in reply to lokibear0803]

It depends on the lesion type. A lymph node e.g. will be determined as affected using a CT image if it has a shape that is more rounded than a healthy node. However, the 18F-DCFPyL can indicate that the lymph node is affected before it has changed its shape. So it is not just a matter of size.

[lokibear0803 in reply to GP24]

Fantastic insight, thank you.

[Tall_Allen]

It means they couldn't see anything that looked like a metastasis in the liver. That may be because it is a false positive or because it is the same density as liver tissue. What does your oncologist suggest? Often, one just waits 6 months and does another CT or MRI.

[lokibear0803 in reply to Tall_Allen]

My MO is asking one of their clinic's radiologists for their interpretation, from analysis of the CD images. I should have insight by end of this coming week.

Your reply gives me cautious optimism, if I'm reading it correctly. Thank you.

[tango65]

All the PET scans are associated with a CT scan to correctly locate where the positive lesions in the PET scan are located. The PET scan has a very low resolution for the anatomy. It is not a calibration CT scan.

The lack of correlation between the PET findings and the CT findings, I believe it means the CT scan does not show anything in the positive area found in the PET scan. It could be a false positive PET scan finding.

Do you know the SUV (standardized uptake value) of the positive area found in the PET scan? If the SUV is low 4 or less most probable a false positive. I had this problem before and the doctors advised to have a 3T MRI scan of the "positive" area.

[lokibear0803 in reply to tango65]

Thank you, Tango65. Unfortunately, for some reason the SUV was not reported. My MO will circle back to them to ask about this.

[tango65 in reply to lokibear0803]

Best of luck!

[Hidden]

Had a similar experience. No SUVmax numbers. Just "indeterminant" and "worrisome." Only correlation was someting in the prostate. .But what they do is radiate it as if it is metastasis.