In radiation therapy, a very precisely targeted radiation beam is aimed at a tumor. The goal is to kill cancerous cells while sparing normal, surrounding tissue. This becomes more complicated when treating tumors of the chest and abdomen, which move each time a patient breathes.
Respiratory gating is a process for continuously monitoring the movement of tumors during normal breathing. Radiation is only delivered when the tumor is exactly in the right place, and the treatment beam automatically turns off when the tumor moves outside of the target field. This technique is used as part of some radiation therapy treatment plans.