SUV Max numbers in PET scan

[Bret5]

I’m currently in triple therapy with metastatic PC after RP 6 months ago. Gleason 10. At time of RP all 12 lymph nodes and bladder neck biopsied tested negative but clearly the cancer escaped and was fast moving. I was re-reading the report on my PSMA PET scan (also had bone scan) and saw repeated references to SUV max values in several different parts of my body. The numbers range from about 5 to as high as 16 in those areas referenced in the report. My understanding is that this basically measures the size of the cancer growth at those locations. My question is, do I have the understanding of SUV max roughly correct, and also, are these numbers typical for metastatic spread prior to start of any medications. Thanks.

[Tall_Allen]

It should be significantly higher than background. Don't try to be a radiologist.

[Bret5 in reply to Tall_Allen]

not understanding your response?

[Tall_Allen in reply to Bret5]

Ask your doctor.

[Justfor_]

You understand it like most people do, including the average doctor, which in principal is wrong. SUV is NOT a measure proportional to size. It is proportional to the density of cancer cells at that spot. A very tiny lesion packed with cancer cells will return a higher SUV compared to the same number of cancer cells scattered around a much larger lesion. That's why when hearing someone quoting dimensions in millimeters, like "PSMA PET scan can only detect tumors larger than X mm", I know he doesn't have the slightest clue about the physics beneath it.

[Bret5 in reply to Justfor_]

thankyou, this helps. What I was really trying to understand is if my numbers in the 5 to 16 range are typical.

[Justfor_ in reply to Bret5]

⁰Values are all relative because there are many parameters that vary, like the sensitivity and resolution of the scanner, the quantity and ageing of the radio ligant (with a half life of -/+ one hour for Ga68 and F18 every minute counts). So, what do they do? There are organs in the body that normally don't host PCa cells but absorb a bit of the radio ligand. Spots on them are selected as reference values for the suspecious ones to compare.

Re your practical question, I have run across posts here claiming that 10 or 12 and above is enough to secure a positive detection. Bellow that there is ambiguity. I don't have a personal opinion on this, just telling you what has been posted here in the past.

[dmt1121 in reply to Justfor_]

Thank you for a very clear answer.

[tarzan11]

My PSMA scan 3 months ago showed values from 3.5 to 35. Cancer on bones from skull to mid thigh. I ask doctor meaning of numbers etc. He looked me in the eye and said " you have a LOT of cancer". I wanted to say " no sh-t Sherlock" but held my tongue. All I know about values is the higher the worse it is.

[MateoBeach in reply to tarzan11]

The isotope for PET scans needs to have a molecule connected to it to bind to the target on the cancer cells, which is the PSMA. The more PSMA That is present, The more isotope will bind to it and show up or light up on the pet scan, this shows the intensity of or concentration of the PSMA at that site. higher values expressed as SUV indicate more PSMA target. This can be useful when selecting treatments like Lu-PSMA (Pluvicto). His scan may suggest that he might be a good candidate for Pluvicto treatment.

[AllenMarco in reply to MateoBeach]

Thank you for this insight. You appear to have much more knowledge about this than many including myself. I just learned, from seeing my PSMA scan reports posted in the portal, that I have new mets to T4 8th rib and "4+ additional new sub centimeter bony lesions with increased uptake. I will see my MO to discuss these findings Monday. I'm glad I saw the report and can get a bit of information before our meeting. We had discussed Pluvecto and I know it is in the bullpen. Please share your thoughts, thanks.

[MateoBeach]

with multiple bone mets you may want to prioritize Ra223 Xofigo which is specific for bone. Then Pluvicto ie looking like a good treatment to follow that. Good luck.

[AllenMarco in reply to MateoBeach]

I didn't give the entire history. I have metastasis to abdominal lymph nodes which have been very slowly progressing, as well as a supraclavicular node. Does this change your thoughts about Xofigo?

[AllenMarco in reply to MateoBeach]

Before I found out yesterday that I have bone metastasis, I was thinking about trying Ostarine to help me with sarcopenia. Again, please give me your thoughts.