Interpreting level of "Mediastinal background activity" in a PET scan report

[Histbuff]

My PET scan results all sound positive but my PSA keeps rising (from 4.20 to 8.49 in 6 months). My findings were apparently summarized as "Mediastinal background activity--1.6". What does that mean? My only SUV given was a 2.5 in a spot that had previously measured 3.0. Thanks for your help.

[Tall_Allen]

It means that nearby healthy tissues are picking up PSMA at close to the rate of the supposed lesion, so they can't unequivocally call that spot cancer.

[tango65]

I believe he is referring to the physiological background radiation of the mediastinal organs, heart and large vessels. The cancer mets should have a SUV larger than the physiological background to be identified.

One has to remember that when the ligand is injected it circulates all over the body and all the organs have some radioactive activity. The metastases having PSMA expression should have a higher activity than the background without PSMA expression such as large vessels , heart etc.

[Histbuff in reply to tango65]

Thank you tango65 and Tall_Allen. I have gotten a headache trying to sort out the different kinds of PET scans. This one was done using Fluciclovine F18. My University of Michigan oncologist suggests that, after a 6-month wait or so, we come back and do a Polifory PET scan. She claims that it is more revealing than my first scan. My problem is that my PSA is making this fast rise but we have no idea why. I have no pains and and I still am leading an active life. I did recently switch my major cancer fighter from Zytiga + Prednisone to X-Tandi. I would love to avoid chemo as long as I can.

[tango65 in reply to Histbuff]

What are the last 3 PSA values?

[Histbuff]

I wish these scores showed a prettier trend: 5.03 (3.16) 5.92 (4.18) 8.49 (6.27)

[spencoid2]

mine are showing a similar trend. next one is three weeks away. a bone scan and CT are showing new bone mets so at least there is a "reason" but the scan interpretations are so hit or miss that the only hope is to have my MO make senses of it. what is your latest doubling time? there are sites (some good some bad) that make it easy to figure out. the best let you put in a series of dates (not just weeks or months) and psa levels

i plot mine to a spreadsheet with a graph and if i have some spare time might add a chart of doubling time but i would have to figure out how excel calculates time in a calendar. probably easier to just use one of the online calculators but i do like charts

[Histbuff]

It's a bit comforting to know that I'm not alone in this interpretive quandary. My doubling time is 4 months. What's yours? I've not had a bone scan or a CT scan for some time because my oncologists seem to think that the PET scan is so much more revealing even though it's easy to get insurance approval for those two but it took 4 months to get approval for my last PET scan. Please stay in touch.