Stock Photo - Male cancer patient lying under a linear accelerator or linac receiving radiation treatment. Radiotherapy is the use of high-energy x-rays (and other rays) to treat cancer. Radiotherapy has to be aimed very precisely to make sure that exactly the right area of the body is treated each time. Patient is wearing a plastic mesh mask that is used during radiation therapy to the head and neck regions. The masks are made from a hard plastic material that becomes very flexible in warm water. When it is wet, it shapes to the contour of your face, then dries quickly and hardens. The masks are important for accurate daily set-up and to confirm the precise alignment of the laser beams.