What your radiologist is recommending is somewhat "old school...!" I mean that's what my urologist and radiologist recommended in 2015-2016 when I had BCR, I argued for including the WPLN and six months ADT based on data from Mayo about BCR for high risk more likely already in the PLNs, they pushed back, I acquiesced, the SRT failed, I was right. Remember, the sensitive imaging we have today was't then.

As samadhi has said, there are other pieces of the clinical data set that may aid in your decision making:

Gleason Score
Grade Group
PSADT
PSAV
Time to BCR

Those still don't say where the recurrence may be, just the likelihood.

A PSMA PET scan may be the critical piece of clinical data you're looking for to aid in your decision making discussions with your medical team. Speaking of that, I would expect a radiologist to say "SRT to the prostate bed...!" Well, not really, mine wouldn't, we discuss multi-disciplinary treatment to manage my PCa. What does your oncologist say? If you are still seeing a urologist, what does he or she say?

For most intermediate and high risk patients, doublet or triplet therapy is more mainstream, at least in terms of NCCN guidelines. There are still challenges and issues with clinical practices adapting those into their clinical practice.

As I say, the questions you have to ask about imaging are:

"Will it inform and change the treatment decision.?
"Will waiting for the imaging (scheduling) or for the PSA to increase to a level, say .5-1 where statistically it increases the chances from roughly 1/3 to 2/3 of locating the recurrence, change the outcome of treatment?

The later is less likely, the former is the critical question.

So, my answer, ask an oncologist, get a PSMA scan, talk with your medical team, radiologis, oncologist and if you feel so inclined, urologist, review the NCCN guidelines, then make your decision.

From the data you describe, I am not sure you are ready to make that treatment decision your radiologist recommends. For myself, blindly radiating the prostate bed and ignoring the likelihood of micro-metastatic PCa would not be my choice, I would want to know where the recurrence is for any decision on radiation and my treatment decision would include systemic therapy for a defined period to account for micro-metastatic PCa.

As to the SEs of radiation, well, I've done SRT, WPLN and SBRT, zero SEs, then again, I'm a study of one, others on this forum are not so fortunate. Why, who knows but I've had the same radiologist for all three, she's damn good as is her team. The sophistication of the planning software and delivery systems is amazing and each team, her treatment plan was subject a peer review board for "approval."

Kevin