Radiotherapy uses ionising radiation to damage the DNA of cancer cells. If the damage cannot be repaired, those cells stop dividing or die. Normal cells can also be affected, but careful planning and their ability to recover help limit harm to healthy tissue.
How radiotherapy is delivered
The most common form is external-beam radiotherapy. A machine directs radiation at a defined area of the body. The machine does not touch you, and the treatment itself is usually not painful.
Other forms include radioactive material placed inside or close to a tumour, known as brachytherapy, and radioactive medicines that travel through the body. The appropriate method depends on the cancer and the treatment aim.
Why treatment is carefully planned
Before external-beam treatment, the radiotherapy team usually creates a planning scan. The cancer target and nearby organs are outlined on the images. A computer plan then arranges the radiation beams and dose.
The aim is not simply to “point radiation at the cancer”. It is to deliver enough dose to the intended target while keeping the dose to surrounding healthy structures within appropriate limits.
Why radiotherapy is sometimes given over several visits
Radiotherapy may be given in one treatment or divided into several treatments called fractions. Dividing the dose can help achieve the desired effect on cancer while allowing normal tissue to repair.
The number of treatments varies widely. A longer course is not automatically stronger or better, and a short course is not automatically less effective. The schedule is chosen for the cancer, the purpose of treatment, the area being treated and the available evidence.
When radiotherapy may be used
Radiotherapy can be used:
- as the main treatment for some cancers;
- before or after surgery;
- with drug treatment;
- to reduce the risk of cancer returning in an area;
- to control advanced cancer;
- to relieve symptoms such as pain, bleeding or pressure.
These aims are different, so the dose, schedule and expected outcome may also differ.
When side effects happen
Side effects usually relate to the part of the body treated and the dose received by nearby normal tissue. Some develop during treatment, some appear in the weeks afterwards, and a smaller number can occur months or years later.
Your team should explain the side effects that are relevant to your individual plan rather than give you a list for every type of radiotherapy.
Questions to ask
- What is the aim of my radiotherapy?
- Which area will be treated?
- How many visits are planned, and why?
- Which short-term and long-term side effects are most relevant?
- Who should I contact if I have problems during or after treatment?
Radiotherapy is a broad group of treatments. The details of the plan matter more than the word alone.