There is a lot of helpful information here about treatment if you want to read further. http://www.cancer.gov/cancertopics/radiation-therapy-and-you/page3
Radiotherapy involves the use of high-energy radiation from x-rays, gamma rays, neutrons, protons, and other sources to kill cancer cells and shrink tumours. Radiation may come from a machine outside the body (external-beam radiation therapy), or it may come from radioactive material placed in the body near cancer cells (internal radiation therapy).
If the primary beam of your radiotherapy passes near your mouth or cheeks, it can have an effect on your mouth tissues. You can discuss this with your oncologist. There are special precautions that will be taken were you to need any form of surgery. As with chemotherapy, it is important you have a thorough check up with your dentist before you start radio-therapy.