Hello, @ddewitt, and welcome. I'm adding your post to the prostate cancer support group, where you might find others who have had a similar experience after radiation therapy.

Here's a little more information about urinary retention after cancer treatment and what treatments are available. https://www.cancer.org/cancer/managing-cancer/side-effects/stool-or-urine-changes/urine-retention.html

It's certainly frustrating to not have any actionable answers for your husband. Has his doctor identified the source of the urine retention?