I think a lot of us have struggled with the thrush. I had it several times throughout my first round of IMRT. I had both the Diflucan and the Nystatin and had success with both like Christine.
I was usually able to tell I was developing thrush by an odd taste in my mouth. The white patches are one of the symptoms but with the IMRT I had those all the time and they weren't necessarily thrush. But every time, I developed an odd taste in my mouth. I can't describe it but it was a noticeable change.

Age 41 - Stage 2 SCC tongue Dx 2/06. Cisplatin x3, IMRT x35. Mets to neck node discovered 7/07. RND 40 nodes removed, margins not clear. Cisplatin, Taxotere, 5-FU Fall 07, then IMXT/Erbitux for 7 wks. Inoperable mets to both lungs and pleura Dx Oct'08. 4 cycles Carboplatin, Erbitux, 5-FU so far.