PET SCANS

A topic that comes up a lot in here and in my groups is "PET scans" - What are they? Do I need one? Will it change my therapeutic decisions? What is the best one to get? where can I get it? What does it cost? Will insurance/Medicare cover it? The following article answers most of those questions.

To ruin the suspense, the best PET scan so far is the F18-DCFPyL PET that was developed at Johns Hopkins and has now entered expanded clinical trials at multiple sites in the US and Canada. But the competition is intense, and several new ones are already in early clinical trials. (There are links provided in the article).

/pcnrv.blogspot.com/2016/12/pet-scans-for-prostate-cancer.html

Thanks, Mel. I know you just had a PET scan, but for the future, UMich is part of the "OSPREY" trial of the F18-DCFPyL PET. It will be running through July 2018.

Thanks Allen.

I just had a recent f18 Pet CT bone scan and had 2 PSMA (DCFBC) as part of a clinical trial last year. Might look into this since JH is close by.

Bobby Mac- LNs are almost never involved for low risk and intermediate risk men. For high risk men, they usually get a bone scan/CT, and use a cut-off of 2% for PLND, and 15% for whole pelvic radiation (called the Roach limit). It's not clear to me that a PET would be useful for that purpose because of the very high probability of false negatives that might result in substantial undertreatment. On the other hand, using numerical cut-offs undoubtedly causes overtreatment. It would be interesting to see a clinical trial based on nomogram values vs PET scans to see which gets better outcomes.

Mel- I haven't seen any such announcement from them, and it would be futile to test the inferior one.

Jerry - I think they developed the DCFBC PET as well, but abandoned it when they improved upon it.

I'm not sure if I understand your question. As you know, the Roach formula is:
(2/3 x PSA) + (Gleason score - 6) x 10 = % risk of PLN mets
and they set an arbitrary cutoff if that's > 15% for deciding whether it's worth LN radiation. It's not set in stone and there are other decision tools.

You've had 50 Gy already, so if that failed, there are a lot of factors to consider (location, time since last radiation, what else is involved, etc.) The small bowel is sensitive to late-term radiation effects and the nodes are near blood vessels that may be sensitive. But there's no point in worrying about every hypothetical - we all can only deal with what comes.

What I meant in engineering terms is that the flow chart is infinite, or at least so large that decision tree analysis is impossible. Everyone's anatomy is different, and everyone exhibits different patterns of metastases, and perhaps most importantly, decision options change with time as we get better medical knowledge and technology. It's not the kind of thing anyone can have prepared decisions for.

E.g. I am Gleason 3+4 and had four LN's before CyberKnife.

George

Tall Allen said...
What I meant in engineering terms is that the flow chart is infinite, or at least so large that decision tree analysis is impossible. Everyone's anatomy is different, and everyone exhibits different patterns of metastases, and perhaps most importantly, decision options change with time as we get better medical knowledge and technology. It's not the kind of thing anyone can have prepared decisions for.

You're right, I suppose. The flowchart does seem to change continually. That alone creates stress. NCCN guidelines are laid out in just such a flow chart format, so at least with some specific knowledge base it is possible at some point to see the available options.

It's hard for me in any context to just saunter along, whistling, oblivious, as the landscape swirls chaotically ahead of me. It reminds me of the City Bending scene in Inception. I should just close my eyes, let whatever happens happen, and then at that single point in time survey the landscape to see just what latest studies guide the next step. My doc will say, "The numbers say x, so we should do y". Then we're off to the races, since I never trust the doctors to have the latest information. Sigh...

I guess that is what we do in the medical arena. We choose a treatment based on what seems right at the moment, what's available, what doctors suggest, what forum buddies suggest, what googled studies suggest, what a constellation of sources coalesce into defining, like planets forming from the swirling gasses of a solar accretion disk.

And yet, another study could come out that same day, saying that the consensed treatment plan is now invalid. Oh well, sucks to be me. Sorry you did that. Should have done something different. Should have done nothing. Should have known better. Couldn't have known better.

I hate it. I just hate it.

Allen said...
Bobby Mac-
I believe you may have read that incorrectly. The purpose of the study you linked was to find the pathological features that might help identify those intermediate risk men who might be at increased risk for lymph node involvement, not to describe incidence. If you read more deeply, you will see that the actual incidence of lymph node involvement among men with pathological GS7 was only 1.8% between 2005 and 2010, which I certainly would characterize as a rare occurrence. The incidence among intermediate risk patients is even lower than that because some of the GS7's were high risk (T3, PSA>20 or tertiary 5s), and none of the GS6s who may have had intermediate risk features (T2b/c or PSA 10-20) were LN+.

Allen -

Thanks, I dug deeper and read what you are referring to on the below link. However, given that the Gleason 8-10 have only an average 12.8% chance of having positive LN's the Gleason 7 1.8% doesn't look that remote to me. Still, as you say it is only 1.8%.

It seems George and myself, both Gleason 7's with positive nodes, have hit some sort of crappy jackpot!

www.archivesofpathology.org/doi/full/10.5858/arpa.2012-0128-OA?code=coap-site

Bobby Mac

Bobby:

I am also in your most esteemed group!

Mel

Mel-

Yes, you are entirely correct in how you read it. The F18-DCFPyl PET scans found a third more distant mets in the same patients than the Ga-64-PSMA-11 scans were able to find. At this point, C-11 Choline isn't even in the same ballpark. F18 certainly seems to be preferable to Ga-64 as a positron emitter, but the challenge had been incorporating into the molecule. Heavy metal positron emitters can be chelated relatively easily, but light atoms (like F or C) must synthesized into it from the ground up. Because of its ridiculously short half-life, you can imagine how expensive it was to have both a cyclotron on site and to have a laboratory machine to synthesize acetate or choline starting with atomic carbon. There is a lot of work on more specific ligands too, so there may be better ones to consider by the time you're ready for your next PET scan.

I didn't go into it in the article, but Cu-64 is a very interesting positron emitter because it also emits beta particles that can kill cancer cells (called theranostic). UCSF and Thomas Jefferson University have been working on a theranostic drug called Cu-64-TP3805 that attaches itself to the VPAC1 receptor on prostate cancer cells. It not only detects where they are but also kills them in the process. (Lu-177-PSMA I&T is similarly theranostic, but is only detected by gamma cameras and doesn't provide as good localization - they often give Ga-64-PSMA-11 with it to aid detection).

With all this talk of C-11s, and Ospreys, and F-18, I thought we were talking about aircraft. :)

The C-11 is the military designation for the Gulfstream2.
The Osprey is a tiltrotor military aircraft, sort of a plane/helicopter hybrid.
The F-18 (actually F/A-18) is an older fighter still around and used by the Blue Angels.

Anyway, God Bless all of our folks in the service of our military.

I suspect the dividing line for having a PET scan or CT to look for affected LNs probably should be at unfavorable risk PC. Bobby Mac was clearly unfavorable intermediate risk (GS 4+3). Mel and George never include a signature, so I can't tell. Unfavorable intermediate risk is anyone with:

(1) GS 4+3 or
(2) GS 3+4 and any of the following:
- percentage of positive biopsy cores ≥ 50%
- PSA 10-20 or stage T2b/2c or both