I'm sorry to hear that 4 years after proton therapy his PSA has only gotten as low as 3.1. I'm assuming he had a Gleason 6 (3+3) or 7 (3+4) score to begin with, because proton monotherapy would be very unusual with higher scores. I'm also assuming that the biopsy did not show signs of hyperplasia or prostatitis that would account for the PSA.What was his PSA history after therapy -- did it plateau at around 3 or did it get to a lower value and then increase to 3? It matters.
Assuming it plateaued and never increased, the most likely scenario is that there is a hypoxic area somewhere in the prostate. Hypoxia -- low oxygen -- can occur in the thick tissue surrounding a tumor. Good oxygenation is necessary for the protons to kill the cancer cancer cells, and cancer cells can survive in hypoxic areas. The biopsy is just a sampling of cells in different places and a 12 core biopsy can easily miss the hypoxic areas where the cancer cells survive. If that is the case, you can do one of two things:
- Continue to biopsy, perhaps doing a saturation biopsy until you find the hypoxic and cancerous tissue. Then you can treat just that area with SBRT or HDR brachytherapy. Or,
- Continue to monitor PSA periodically. If the PSA never increases, the cancer may be indolent, and may never be a further cause of concern.
Unfortunately, proton therapy delivers a lifetime maximum dose of radiation to the prostate and a margin around it, so you can't re-treat the whole local area; however, if it is possible to locate the cancer in the prostate, the prostate bed or lymph nodes, you can spot treat just that place with SBRT or HDR brachytherapy.
When you wrote "he had a scan after isotopes were administered," wasn't that a PET scan, or was that a contrast MRI? There are several types of PET scans, but I do not know if they would show anything with a PSA of just 3. An ordinary bone scan is much too insensitive for very small tumors, but one of the newer ones like Prostascint, F18Choline, or NaF18 (there are a few others that are not commonly available) may be worthwhile. If you have access to the Mayo clinic, or a handful of other specialty places, you may be able to get a C11Choline PET scan, which is much more sensitive. Feraheme MRI is in clinical trial at SandLake Imaging in FL, but I have no idea if it can pick up anything in and around a proton-radiated prostate. I don't know if they've had any experience with that, but you can call.
If his PSA has been rising and you can't locate it in the local area, it is possible that it has metastasized. In that case, hormone therapy may be required to slow its spread.
I'm hoping that it is just some indolent cancer in a hypoxic area that only needs watching.