Radiotherapy treats cancer by using high-energy x-rays to destroy the cancer cells, while doing as little harm as possible to normal cells in the surrounding area such as the bladder or back passage (rectum). Radiotherapy for locally-advanced prostate cancer usually uses a machine similar to a high-powered x-ray machine (external beam radiotherapy). Your doctor may suggest that you have hormonal therapy before or after your radiotherapy.

The treatment is given in the hospital radiotherapy department, usually as daily sessions from Monday to Friday, with a rest at the weekend. For locally-advanced prostate cancer, radiotherapy will be given for 4-7 weeks.

Planning is a very important part of radiotherapy and may take one or two visits. The treatment has to be carefully planned to make sure that it is as effective as possible. You will be asked to have a CT scan or lie under a machine called a simulator, which takes x-rays of the area to be treated. The treatment is planned by a cancer specialist (clinical oncologist).

Marks are usually drawn on your skin to help the radiographer (who gives you your treatment) to position you accurately and to show where the rays will be directed. These marks must stay in place throughout your treatment. Permanent marks (like tiny tattoos) may also be used. These are very small and will only be done with your permission. You may feel a little discomfort while they are being done.

At the beginning of each session of radiotherapy, the radiographer will position you carefully on the couch and make sure you are comfortable. During your treatment you will be left alone in the room, but you will be able to talk to the radiographer who will be watching you. Radiotherapy is not painful, but you have to lie still for a few minutes while the treatment is being given.

Conformal radiotherapy (CRT) or intensity modulated radiotherapy (IMRT) are increasingly being used, although these are not available at all hospitals.

In conformal radiotherapy (CRT), a special attachment to the radiotherapy machine carefully shapes the radiation beams to match the shape of the prostate gland. Shaping the radiotherapy beams reduces the radiation received by the healthy cells in nearby organs such as the bladder and rectum. This reduces the side effects of radiotherapy and may allow higher doses to be given, which could be more effective.

Intensity modulated radiotherapy (IMRT) is a newer, more complex type of conformal radiotherapy that allows the radiotherapist to vary the dose of radiation given to different parts of the tumour and surrounding tissue. It is not yet known whether IMRT is better than conformal radiotherapy.

Radiotherapy to the prostate can make it more difficult to have an erection. There are various treatments which can help (see dealing with side-effects).

Radiotherapy to the prostate area may irritate the rectum, and cause discomfort and diarrhoea. It may cause soreness around the anus. Your doctor can prescribe medicines to reduce this and you may be advised to change your diet.

The radiotherapy may also cause cystitis, which can make you want to pass urine more often or cause a burning feeling when you pass urine. Your doctor can prescribe medicines to reduce this. These effects usually disappear gradually a few weeks after the treatment has ended. Rarely, if you have difficulty in passing urine, it may be necessary to have a urinary catheter put in.

Radiotherapy can also cause general side effects such as tiredness, which are mild for some men and more troublesome for others. The radiographer will be able to advise you what to expect. Try to balance rest with regular, gentle exercise, especially if you have to travel a long way for treatment each day.

The radiotherapy may make some of your pubic hair fall out. When you have finished the course of treatment, the hair will grow back. However, the hair may be thinner or finer than it was before.

Most side effects of radiotherapy gradually disappear once the treatment has ended. However, others may continue for some months and some may even be permanent. If you have any problems during your treatment, talk to the radiotherapy staff as they will be able to help you.

Radiotherapy does not make you radioactive and it is perfectly safe for you to be with other people, including children, throughout your treatment.

Our general information section on radiotherapy gives more details about this treatment and its side effects.

Radiotherapy to the prostate area can sometimes lead to long-term problems.

Radiotherapy for prostate cancer can cause an inability to have an erection (impotence) in about 3-5 in 10 (30–50%) of the men who have this treatment; this may develop over a period of 2–5 years. Our page on dealing with side effects discuss ways of coping with erection problems. This side effect of treatment can be very difficult to deal with and can affect your sex life and your relationship with your partner. You may find it helpful to read our section on sexuality. Many organisations offer counselling for sexual or relationship problems.

In a number of men, the bowel or bladder may be permanently affected by the radiotherapy. The blood vessels in the bowel and bladder can become more fragile and this can make blood appear in the urine or when you pass bowel motions. This can take many months or years to occur. If you notice any bleeding, it is important to let your doctor know so that tests can be carried out and appropriate treatment given. Occasionally bowel movements may be more urgent after radiotherapy and, rarely, there may be some difficulty in controlling the bowels.

Often, radiotherapy can help to improve problems with passing urine, but for some men radiotherapy can lead to leakage of urine due to damage to the nerves that control the bladder muscles (urinary incontinence). This is unlikely unless you have had a TURP or prostactectomy as well. If this happens it is important to discuss it with your doctor, who can arrange for you to see a specialist continence nurse. You may also find it helpful to contact the Continence Foundation.

If radiotherapy has been given to the lymph glands in the pelvic area as well as to the prostate, it can cause some swelling of the legs, known as lymphoedema.

We have further information about the long-term side effects of pelvic radiotherapy.