How do gamma rays treat cancer without making people ill?

Kill cancer cells.: Radiation treatment for cancer consists of multiple, concentrated beams of gamma rays directed at the tumor to kill the cancer cells. These are directed at different angles in order to concentrate the rays on the cancer while minimizing damage to the surrounding normal tissue. They pass through the body, causing dna damage to cells. That's why they are used to treat internal tumors, like brain.

Targeting: Radiation oncologists are trained to precisely deliver radiation to specific areas. The goal is to focus the energy on the tumor while limiting how much damaging radiation reaches otherwise healthy tissue. The beams are often arranged at positions to prevent undesirable overlap. Ct scans are usually used to plan exactly how the radiation will be delivered in order to maximize the safety.

Focusing: Gamma rays from multiple sources are focused on the lesion, thus reducing the damage to normal tissues.

Gamma rays are a: Single energy from an isotope like cobalt 60, used in the gamma knife. It is a photon. High energy x-rays are spectral - and these can be delivered by linacs. Sophisticated beam arrangement are done by treatment planning, intensity modulated (imrt) or conformal. Puttng energy into tumor target/avoid tissues that don't need it. Old methods didn't do this.