Hi Nellie,
I suspect that each ENT has developed his/her own timing for post-treatment follow up. After radiation, my ENT wanted to see me every 6 weeks for the first year with CT scans every 3 months. Then every 8 weeks for the second year (CT scans every 6 months) and every 12 weeks the third.

If you're uncomfortable having to wait 3.5 months, see about moving the appointment forward. Waiting and uncertainty are anxiety producing and you shouldn't have to endure that if at all possible. Hoping that all goes well. - Sheldon