I'm in the same boat. My first follow up examination on 9 Jan seemed to show no tumour (treatment finished 5 Dec 2012). Had an MRI scan on 4 Feb the result of which I was told 'doesn't look normal' but there could be scar tissue or liquid, or at worst cancerous activity. My original tumour was 4.5cm at stage 2b, whatever is there is about 1.5cm.
My consultant says she thinks they did the scan too early (exactly 2 months after last rads) so has booked me in for a PET scan on 11 March.
I have been to hell and back in the last couple of weeks, imagining all sorts of things and dreading that I might need a pelvic exentoration. Trying to keep positive!