Person undergoing radiotherapy on a linear accelerator to treat Hodgkin's disease, a cancer of the lymphatic system. The illuminated discs over the patient's chest indicate the areas which are to receive radiation. The pattern is defined by an arrangement of lead blocks suspended below the head of the accelerator, which shields the lungs from excessive irradiation. Linear accelerators are used as a source for high- voltage X-rays, which have the ability to penetrate the skin to a greater depth and deliver a larger X-ray dose to the target area relative to the dose at the skin.