Radiation oncology is the science of treating cancer with beams of radiation. Although radiation itself causes cancer, radiation is very destructive to cancerous tumors. By carefully shaping and moving the beam through the patient, radiation can be concentrated on the tumor, thereby reducing the damage to surrounding tissues. The beams are produced by huge machines known as linear accelerators. For the sake of safety, accelerators are verified daily to ensure they are within the expected parameters. This process is known as a daily constancy check. The science of radiation measurement is called radiation dosimetry.