The Candida (thrush) will not really be a factor for awhile, though as his immune system becomes weak from the radiation later in treatment, it will likely appear. Most of the complications related to treatment are discussed in the dental section of the main web site, or you can use this link
http://www.oralcancerfoundation.org/dental/dental-complications.htm to get there. Candida is specifically discussed here:
http://www.oralcancerfoundation.org/dental/candida.htm I would also search the message board, (all forums), for the words thrush and Candida, as it has been discussed many times. The search engine for the message board is located at the top of the first page next to "my profile". The search engine for the main web site is located on each page which has a navigation bar at the bottom of the navigation links. If you still have questions after checking this out please ask them here. Many of us have awakened with the infamous "white tongue" and can help you further.