Every treatment using radiotherapy has to be rigorously planned. The planning process consists of three phases:
Radiotherapy Treatment Planning Planning
The cancerous tumour has to be located so that its size and position can be analysed. This information can be obtained from:
Radiotherapy Treatment Planning Simulation
Once the amount of radiation to be given has been accurately calculated, the patient then goes to the simulator to determine what settings are to be selected for the actual treatment using a linear accelerator.
The settings are determined by taking a series of x-rays to make sure that the tumour is in the correct position ready to receive the ionising radiation.
Radiotherapy Treatment Planning Treatment
Irradiation using high energy gamma rays.
Irradiation using high energy x-rays.
Cancerous tumours can be treated using radiotherapy as follows:
Gamma rays are emitted from a cobalt-60 source – a radioactive form of cobalt.
The cobalt source is kept within a thick, heavy metal container.
This container has a slit in it to allow a narrow beam of gamma rays to emerge.
Radiotherapy Treatment Irradiation Using High Energy X-rays
The x-rays are generated by a linear accelerator (linac).
The linac fires high energy electrons at a metal target and when the electrons strike the target, x-rays are produced.
The x-rays produced are shaped into a narrow beam by movable metal shutters.
The apparatus is arranged so that it can rotate around the couch on which the patient lies.
This allows the patient to receive radiation from different directions.
The diseased tissue receives radiation all of the time but the healthy tissue receives the minimum amount of radiation possible.
Treatments are given as a series of small doses because cancerous cells are killed more easily when they are dividing, and not all cells divide at the same time – this reduces some of the side effects which come with radiotherapy.
This involves placing implants in the form of seeds, wires or pellets directly into the tumour.