SUVmax PSMA F18 PET/CT Scan

[MGBman]

2015 RP, 31 x EBRT, two yrs ADT. A few days ago I had my second PSMA F18 PET/CT scan (I’m on a trial). First one was May 2020. First scan PSA was 1.5, second scan PSA was 6.9. Both scans only detected one tumour in location of where my right seminal vesicle used to be and no other tracer avid involvement ( I do realize that PET scans do have their limitations). My SUVmax in the first scan was 3.3 and recent scan was 11.6. Unfortunately, the radiology report only gave one dimension of 1.2 cm for the tumour (as opposed to the first scan report of 2cm x 1.2cm x 1.3cm). In discussion with my oncologist, I neglected to ask her what is the ‘so what’ of the change in SUVmax 3.3 to 11.6. I suppose common sense would indicate that the tumour has enlarged but not necessarily metastasized. Any thoughts?

[Tall_Allen]

You are correct that a tumor in the prostate bed doesn't suggest a metastasis.

It's either:

(1) A false positive because PSMA is excreted by the urinary tract. But it's appearance on both scans increases the likelihood that it is residual cancer, or

(2) Some residual cancer that survived your SRT. An mpMRI is actually a better way to detect it, and a biopsy is still better. If it is real, a single insertion of focal HDR brachytherapy or focal SBRT may annihilate it.

[MGBman in reply to Tall_Allen]

Thank you Tall Allen for your response. Yes, I have had two mpMRIs as my oncologist thought I was a candidate for needle based brachytherapy. Unfortunately, after the PET and MRI scans the location of my tumour will not permit any further radiation no matter how it is given or surgery so I am left with ADT again. Shortly to start on degarelix. I was just wondering about the change in SUVmax values and if that indicates a more serious tumour. I have asked to have my recent PET scan to be reviewed by a second radiologist. I know it will not change my treatment but simply from a professional perspective I have to ask. I have copies of my various scans (less the current scan) and have had the tumour pointed out to me and it definitely sticks out like the proverbial sore thumb. As I live in Canada, our options are less than many other countries.

[Tall_Allen in reply to MGBman]

It is very unusual that a single dose of HDR brachy can't be inserted there if it is where your seminal vesicle was. Is there an HDR brachy specialist you can get a second opinion from? If you are near Toronto or Vancouver, there are specialists.

[MGBman]

Interesting you ask. My oncologist is one of the top brachytherapists and has an international reputation…written or co-authored 200 plus articles. The problem as I understand it is the location of my tumour. I can clearly see it on the various scans so my simple soldier mind wonders why it can’t be removed surgically let alone attacked with needle based (not seeds) HDR. My oncologist initially thought that such an approach was possible until the scans revealed otherwise. The risk of damage to either my bladder and/or rectal wall apparently is too high and I did say that I could not live with either a permanent catheter or colostomy in case of a misfire. I think that may have a had an impact. I thought surgery would be possible, but again, the experts (except one) all said that after so much radiation, resection was not possible. It has been suggested by a top urologist in Toronto and Miami that a biopsy might reveal more useful info and that cryotherapy might be possible. Again, if you can’t resection or hit the tumour with brachytherapy needles how can you find it to biopsy it. As a retired soldier I find it very difficult and frustrating to conduct active surveillance all the while watching my enemy get bigger and stronger and simply waiting to return to ADT as the only solution. Anyway, thanks for listening and I’m still curious about the SUVmax question.

[Justfor_]

There is a recent video interview with a PSMA PET specialist. TA was the interlocutor posing the questions. At the question regarding the minimal detectable dimension (4 or so mm with a digital scanner, or a bit more with an older analog one) he dismissed the subject altogether. He said that it is not a question of dimension but of PSMA concentration. To make his point he claimed that a one mm lesion very PSMA avid may show up in the scan while a lesser avid one of 10 mm may not. In your case, SUVmax is indeed a metric of the PSMA spatial concentration, whatever this may medically indicate.

[MGBman in reply to Justfor_]

Thank you Justfor. I checked youtube and there are quite a few videos about PSMA PET. Do you happen to know the Doc/specialist's name?

[Justfor_ in reply to MGBman]

The name is Andrei Iagaru.

You will find the youtube link here:

healthunlocked.com/prostate...

The part I mentioned is at the ~29th min mark, but the entirety of the interview is worthy.

It is a more in depth view than the usual simplistic and some times grossly inaccurate blah-blah you may receive from silly/ignorant doctors.

[MGBman in reply to Justfor_]

Thank you. I will watch the video.

[tango65]

I would try to get Lu177 PSMA treatment abroad if financially possible. Germany and India have a better Covid 19 situation that the one we have in the USA. The LU 177 is a systemic treatment and it will treat the PSMA lesion in the PF and any other lesion.

[MGBman in reply to tango65]

Thank you Tango65. It would appear as though my only real option, aside from ADT, would be something like Lu-177 and/or one of the 2nd generation of drugs (which my oncologist does not want to do just yet). Yes, the down side of the Lu-177 is the significant cost. I checked a few places and it also seems that one has to be castrate-resistant which I am not as yet. If I went down the 177 road, I would prefer somewhere in the US. I'll have to do more research. I finished my first ADT five yrs ago and about to start on degarelix. Have no idea how soon I will become castrate-resistant....something that I'm not really looking forward to. Possibly better to stick my head in the sand and it will all go away.

[tango65 in reply to MGBman]

There is a clinical trial with Lu 177 PSMA for oligo metastatic hormone sensitive cancer in the USA, perhaps you may qualify:

clinicaltrials.gov/ct2/show...