Jeani,
With me it was about the same. ENT didn't want to call for a PET until a year after RT. RO called for one about 5 months out and it wasn't useful, because I was still too "hot" from the treatments.
ENT checked me monthly, in the same manner as your husband. Everything was fine until 10 months past RT they found a "soft spot", byopsy proved SCC present, so I'm off to surgery again and back down that road.
They really didn't think mine had or would spread to other areas of my body, which is why each check up consentrated on the ear, nose, throat areas. After my second byopsy it proved them correct, the only cancer "hot spots" in my entire body where the two in my mouth....good luck...