To get the maximum benefit from radiotherapy treatment planning must be very careful. This task must be to radiotherapy. It is essential that every treatment session will take the same position on the couch. To facilitate this operation, before starting the treatment may be necessary to build a special mask plastic to protect parts of the head and neck that should not be irradiated. This if, during the first visit to the center of radiation takes the imprint of the face and neck. The next time you are asked to wear the mask and lie on the couch under a special machine, called the simulator, or under the scanner with which you run the TAC for take radiographs of the area to radiate. The area to be irradiated is marked by drawing on the mask special signs with a marker.