Hi Ann,
as above, a follow-up scan would only usually be done if your husband starts to get pain or other symptoms which would indicate a progression.
Using my own case as an example, I had several mets on my bones at diagnosis back in 2019. After chemo (Docetaxel) and radiotherapy in 2019, my follow-up for the next 3 years was based purely on PSA readings at my 3-monthly meetings with my consultant. I had no symptoms, no pain and PSA was under control, so no scans.
However, in January 2023 I started getting acute sciatic pain flares. I was quickly booked in for MRI and CT scans, which showed a met on my spine had grown and was interfering with the sciatic nerve root. I had a couple of sessions of RT which sorted it temporarily, with further sessions being planned.
It's good that your husband is feeling well and keeping active, long may that continue. If my experience is anything to go by, if his situation changes then scans and follow-up treatments will get done very quickly.