Radiotherapy is the use of controlled, high-energy radiation, usually X-rays, to destroy cancerous tumours. The treatment doesn't make you radioactive and it's perfectly safe to be with others during the course of your treatment.

If you have been diagnosed with cancer in your rectum, radiotherapy may be offered to you as a treatment option. It is usually given at the same time as chemotherapy, as this makes the cancer cells more sensitive to the radiation. Chemotherapy and radiotherapy together is known as 'chemo-radiation'. Radiotherapy is not usually used to treat cancer in the colon.

Chemo-radiotherapy is an effective alternative to surgery for anal cancer. Please see our 'Anal Cancer' factsheet for further information.

How is radiotherapy given?

Radiotherapy can be given in two ways:

  • External radiotherapy is delivered from outside of the body by a machine and only takes a few minutes. The intention is to reduce the side-effects to healthy tissue of giving all the radiation in one go. During each treatment session, a 'fraction' of radiation is given, which will equal the full dose by the end of the course.
  • Internal radiotherapy involves positioning radioactive sources inside or near to the tumour.  The main advantage of this treatment is that it can deliver a high dose of radiation directly to the cancer while limiting damage to surrounding tissues and organs. This treatment, also known as brachytherapy or contact radiotherapy, is not currently available at all cancer centres, and you may have to travel to a specialist centre.

Radiotherapy can be used at several different stages of treatment:

Pre-operative radiotherapy

Radiotherapy can be given before surgery (also known as neo-adjuvant radiotherapy) to:

  • Shrink the tumour in order to make it easier to remove
  • Reduce the risk of the cancer coming back ('recurrence') after your surgery

If you are prescribed external radiotherapy, the treatment could either be a short course (eg five treatments over a period of five days) or a long course (eg five treatments a week, for five or six weeks). The length of the treatment will depend on the size of your tumour.

If prescribed internal radiotherapy, this treatment usually takes one or two sessions.

Whether you have external or internal radiotherapy, there will be a period of time between the radiotherapy treatment ending and your planned date for surgery. This delay is intentional, as the radiotherapy continues to shrink the tumour for several weeks after the end of treatment.

Post-operative radiotherapy

If you have not had radiotherapy before your surgery, you may be advised to have external radiotherapy in conjunction with chemotherapy after surgery (also known as 'adjuvant radiotherapy'):

  • To destroy any cancer cells that may be left behind
  • If the tumour was difficult to remove
  • If your cancer has grown through the wall of the rectum or spread to nearby lymph nodes

The course of treatment may vary from five to seven weeks, five days a week.

Palliative radiotherapy

Lower doses of radiotherapy, over a shorter period of time, can also be given if surgery is not an option to:

  • Relieve symptoms
  • Slow the spread of the cancer

If your clinical oncologist believes you will benefit from radiotherapy, they will discuss the proposed treatment plan with you. Ask your doctor about what they are recommending for you, how the radiotherapy will be given and the choices you have.

Specialist radiotherapy techniques

Radiotherapy and other similar technologies can also be used in novel ways to treat metastases that may have developed in other parts of the body eg the liver, brain or lung. These very special techniques can only be carried out in a few specialist centres around the UK, but they may offer individual patients a viable alternative to surgery, if the tumours cannot be removed safely by surgery. There are a number of ways these new techniques are used, and you may hear them referred to as IMRT (Cyberknife) and RFA (Radiofrequency Ablation). For further information, please download our booklet 'Treating Bowel Cancer -  Your Pathway'.

Side-effects of radiotherapy

The side-effects of radiotherapy will vary depending on length and intensity of treatment you have. It will affect the bowel and other local tissue, including your skin and other tissue close to the tumour. This can cause temporary pain,  discomfort, and change your bowel habit. Your radiology team will be able to advise you on how to minimise and cope with any problems or side-effects associated with your treatment.

Please read here about the possible long term side-effects and how to manage them.

Last reviewed 17/3/14

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