The radiation is delivered by a machine called a linear accelerator, or linac. Most linacs have a gantry, which is the head of the machine. The gantry houses a device called a multi-leaf collimator that "shapes" the radiation beam so it conforms to the shape of the tumor from any given angle. During your treatment, the gantry will move around you to deliver the radiation. The radiation beam is not visible to the eye, so you will not see it when it leaves the gantry.
Respiratory gating is sometimes used during radiation treatment for lung cancer. This technique enables your team studies the motion of your chest as you breathe. A small cube called a chest block is placed on your chest to monitor the position of your lungs and your breathing cycle. The chest block transmits a signal to the control room, where your radiation therapist can observe the pattern of your breathing and control the delivery of the radiation. The chest block tells the therapist if you’re breathing the same way as you were during imaging, or if the timing of the radiation beam needs to be adjusted to make sure that exposure to sensitive organs is minimized. Your team may also take additional scans to see if your internal organs or the position of the tumor have shifted. Both pieces of information — your breathing and the position of your organs — need to be captured at the same time in order to deliver the most accurate treatment possible.
Your first two treatments may take 15 minutes or more, as your radiation therapist helps you get into position and takes images to verify that your setup on the machine is the same as the treatment plan. Subsequent treatments, however, are often shorter. In fact, some treatments — from entering the waiting room to leaving the clinic — can take as little as 12 to 30 minutes.