Patients undergoing radiation treatments are required to undergo a process called simulation to accurately identify the area that needs to be treated. During simulation an x-ray study is done to locate the area that needs treatment and then lasers are used to allow marks to be placed on the body. When treatment occurs later, lasers are used to assure the patient is in exactly the right position for treatment. Many times, special devices are made to help hold the patient in the correct position. Sometimes special molds are made that fit closely around key parts of the body. For head and neck cancer or when the brain needs to be treated, customized mesh masks are made to accomplish the same thing. Collectively these are known as immobilization devices, something to prevent movement while the treatment is being given.