Sealed source radiotherapy

Sealed source radiotherapy or brachytherapy is the application of radiation from close range and is used for techniques where the radioactive source is placed inside the area requiring treatment.
The greek word "brachy" means close or nearby, and is the opposite of "tele" which means far or at a distance.

In cancer medicine, the cancer needing treatment can be in the lining of a tube like the esophagus or 'food tube', in which case a radioactive source can be lowered into the esophagus and left there to irradiate its X-rays into the cancer (assuming the source is placed next to the cancer!).

Or it could be an internal organ like a muscle. Obviously there are no natural tracks leading into muscles so radiation oncologists create them by using hollow steel needles. Once placed, the radioactive source can be slide inside to irradiate the area required.

Or it could be a large flat area like the skin. There is no need for any holes to be made, so the radiation oncologist can use a mould (a wax block with hollow tubes inside to take the radioactive sources) to place over the skin.