I am sorry to read about RP failure. The info you shared is evident of recurrence and you are now facing the need to decide on a salvage treatment. It may help to read about the experiences of others. Type this in a search engine: You Are Not Alone Now.
My case was similar to that of your husband’s, however my experience was 12 years ago when techniques and tests were different than the ones at present.
Back in 2000 (50 y/o) three weeks after surgery the first PSA was high at 0.18 and recurrence was declared at the 6-month mark with a PSA of 0.42. I was positive for extra capsular extensions too.
All scans were negative and doctors (MSKCC, JH, Japan) diagnosed me with Micrometastases. This is a condition where cancer forms colonies of tiny tumours difficult of being detected by traditional scans (CT, MRI, Bone scan). I looked for other means to locate the cancer (so that I would have it as a target where to direct radiation) but earlier (2001) Prostascint and PET scans were considered “impractical” because of the many false positive results. It seems that the cause was due to poor contrast agents and techniques used at that time. Now I also know that the resolution of the equipments do not catch small tumours with sizes of lesser than 1.5 to 2.0 mm.
Because of the low Gleason of my case (2+3), doctors recommended me Watchful Waiting (similar to the Active Surveillance of those times), and so I waited until 2006 before committing to salvage radiotherapy, even with negative image studies. I did SRT with a starting PSA of 3.8 ng/ml and that took me to a nadir of 0.05 at 13-months post RT.
Recurrence became apparent again in 2010 which lead me to start hormonal treatment. You can read about my events after that in this link;
Newer contrast agents and testing techniques with crisscrossing information (PET + MRI or CT) or (MRI + MRSI) seem to give better results in image studies but they all require a certain tumour “size”. As commented by Allen there is a lot of uncertainty once one recurs from a major treatment. No one can say that by choosing a different approach the results would be better.
Doctors also do not know what exactly may be the outcomes from their suggestions and everything resumes to guessing. Their recommendations are based on past experiences from similar cases but no two cases are equal in prostate cancer affairs.
I would recommend you to consider Quality of Life and that you do researches on the side effects. They tend to superimpose the ones already in place. There are always things that one would not like to lose or trade.
You should also get second opinions from specialist in all fields. A radiation oncologist and/or medical oncologist may be proper for consultations on following treatments. Your husband got enough time to go through before commiting to any protocol. Do things coordinately and timely.
Wishing you find a decision suitable to both of you and the best of lucks.