External beam radiation does not make you radioactive. It passes through you like an x-ray. It does not stay in your body. That’s why it’s safe for you to be around other people, even children.
External beam radiation therapy is targeted to only treat the cancerous cells and to stay away from your body’s healthy cells.
It is not like when you turn on a light switch and the light fills the whole room. Radiation is precise in the way that it is delivered.
The machine delivers radiation only to a prescribed area. This is why you do not need external shields to stay safe.
Click to enlarge image.