Radiotherapy is a treatment that involves the use of high-energy radiation, usually X-rays. It is one of the most common treatments for cancer; almost half of all people with cancer have radiotherapy as part of their treatment plan. Radiotherapy destroys the cancer cells in the treated area by damaging the DNA within these cells. Although normal cells are also affected by radiation, they are better at repairing themselves than the cancer cells. For this reason, radiotherapy is planned to be given over a number of sessions, on daily basis and can last for few weeks, so that the patient recovers from the dose given the day before.
Doctors plan the treatment to give a high radiation dose to the tumour and a small margin around it. The treatment is also planned to give as low a dose as possible to the surrounding healthy tissue to reduce the risk of side effects. Achieving a greater accuracy is one of the main goals for radiotherapy research, because it causes less damage to healthy cells, delivers a stronger radiation dose to cancer cells, and makes the treatment shorter and more effective.
Advanced treatment methods, such as intensity-modulated radiotherapy (IMRT) and image guided radiotherapy (IGRT), allow doctors to plan the radiotherapy treatment area very precisely by shaping the radiation beams around the area of the cancer. In IMRT, each radiation beam is broken up into ‘beamlets’ with individually controlled intensity of radiation to fit tumour shape and biological characteristics.
The tumour shape and location can change between the treatment sessions. IGRT method uses CT scan and other scans (such as MRI scans and PET scans) before and during radiotherapy treatment to show the size, shape and position of the cancer as well as the surrounding tissues and bones. The repeated imaging scans during the course of treatment allow doctors to position the patient accurately or to adjust the plan (tweak beams) as needed, in order to deliver higher radiation to tumour and to spare healthy cells.
For more information about radiotherapy, how it is performed, and its side effects, please refer to the following links:
- A new animation, released in 2016, shows how targeted doses of radiotherapy can be administered
- An animation shows how the rectum changes from day to day.
- An interactive radiotherapy treatment simulation (requires Flash).