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F18 or gallium 68

User
Posted 31 May 2021 at 09:05

Hello all I've got a PSA of 0.88 and a doubling time of 5 months. My last test was in late march. My prostatectomy was in 2016 and radiotherapy in 2017. My oncologist referred me for a gallium 68 scan at UCL in September when my PSA was 0.3 but it failed to find anything. He's booked me for a f18 scan ( which has only recently become available there ) at my local hospital in Brighton in July. The intention is to possibly give me further radiotherapy with the aim of putting the cancer into remission. My question is, do any of you know how f18 compares with gallium? I'm guessing that gallium would not be an NHS option for me this time

User
Posted 31 May 2021 at 13:45

I think it's mainly down to the logistics of producing the radioisotope, locally or remote and shipped in. The 18F is newer and has a longer half-life. It has a theoretical imaging advantage too (should be higher resolution), but I haven't seen anything that says this shows this up in practice.

Each cyclotron run produces enough 68Ga for about 4 scans (when it works, which it often doesn't), but with a half-life of 68 mins, you've lost half of it if it takes 68 mins to transport to the facility or wait for the scanner (as it can't scan 4 people at once). 18F has a half life of 110 mins and I believe is easier to produce locally, which makes it logistically more interesting. I don't know how many doses are produced at once, but if you have a queue of people waiting to go through your scanner, it will remain viable for a longer time.

User
Posted 31 May 2021 at 14:52

Thanks that's helpful. I just wanted to check that its a good scan and not worth paying for a private gallium one

User
Posted 31 May 2021 at 15:00

I would recommend asking a radiologist or diagnostic radiographer. It's still quite new and my information might not be the latest state of play.

User
Posted 31 May 2021 at 15:45

Originally Posted by: Online Community Member

I think it's mainly down to the logistics of producing the radioisotope, locally or remote and shipped in. The 18F is newer and has a longer half-life. It has a theoretical imaging advantage too (should be higher resolution), but I haven't seen anything that says this shows this up in practice.

Each cyclotron run produces enough 68Ga for about 4 scans (when it works, which it often doesn't), but with a half-life of 68 mins, you've lost half of it if it takes 68 mins to transport to the facility or wait for the scanner (as it can't scan 4 people at once). 18F has a half life of 110 mins and I believe is easier to produce locally, which makes it logistically more interesting. I don't know how many doses are produced at once, but if you have a queue of people waiting to go through your scanner, it will remain viable for a longer time.

Not quite right there Andy.  68Galliam is produced by a ' Generator' not a 'Cyclotron' 

Also what 18F scan is on offer, as there are several including 18F PSMA 107 and  18F DCFPyL ? In comparative  tests the last one showed more sites than the 68 Gallium scan.  It is good if this scan is now available in the UK.  Hitherto it was only available in the USA  (where it was produced by Martin  Pomper and his team at John Hopkins), and in Canada. 

So OP needs to be more specific regarding 18F  

Barry
User
Posted 31 May 2021 at 16:49

I'm not sure if this is specific enough but on the online leaflet it say f18 FDG pet CT scan

User
Posted 31 May 2021 at 18:26
There are so many tracers now, each of which works in a slightly different way. Gallium 68 is considered to be the most sensitive at very low PSA levels but some prostate cancers just don't show up on Ga68. F18 FDG isn't as popular for prostate cancer because much of the tracer is cancelled out by the kidneys so it doesn't get to the prostate, but F18 FDG seems to be very good at picking up mets. Then there is F18 FACBC (Axumin) which is what was being trialled at Leeds following excellent results in Italy, and there is also 18F DCFPyl which is good at picking up recurrence in the prostate / prostate bed.

These all seem to be more efficient than the standard choline tracer but each is slightly better for picking up cells in certain circumstances. If your Gallium scan didn't pick anything up, it may be that the mets are so tiny and so widespread that no tracer is going to see them yet; on the other hand, your particular prostate cancer may be more responsive to an 18F or F18 than it was to a Ga68

"Life can only be understood backwards; but it must be lived forwards." Soren Kierkegaard

User
Posted 31 May 2021 at 22:06
OK, it's not the18F DCFPyL scan being offered but the F18 FDG. As Lyn says, suitability can vary with patient, and I think best decided by Oncologist/Radiologist. About 8% of men do not express sufficient PSMA for the 68 Ga scan to work for example. An important factor generally is where any escaped cancer cells might have migrated to and whether these are in concentrated clumps or are more finely distributed. That latter makes it difficult to locate as you would expect, even with the best scans.
Barry
User
Posted 31 May 2021 at 22:07

Thanks for the corrections Barry. I did think my response was probably not up-to-date.

 
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