Side effects of external beam radiotherapy

Radiotherapy to the prostate may cause a number of side effects. These usually disappear once treatment has finished.

Side effects during treatment may include tiredness, irritation of the rectum and diarrhea. You may also have some inflammation of the bladder (cystitis) so you may have some pain passing urine. Let your doctors and radiographers know about any side effects you have so they can help manage them.

Some side effects may not get better over time or they may develop some time after having radiotherapy.

Radiotherapy can cause problems with getting and maintaining an erection (erectile dysfunction or ED). This may not happen until sometime – 2-5 years – after treatment. Ask your oncologist about your likelihood of developing ED. There are various treatments that can help manage ED.

Other long term problems include infertility, and bladder or bowel problems. 

It is important to talk to your healthcare team about either short- or long-term side effects. There are often ways to help manage them.

Short-term side effects

Most of the side effects of external beam radiotherapy gradually disappear once treatment has finished. Your cancer specialist, nurse or radiographer can tell you what to expect. Tell them about any side effects so that they can help manage them. Radiotherapy causes tiredness, especially if you’re travelling a long way for treatment each day. Try to make sure you get enough rest, but balance this with regular, gentle exercise, which will give you more energy.

Radiotherapy to the prostate area may irritate the rectum, cause soreness around the anus, and cause diarrhoea. Your doctor can prescribe medicines to reduce these effects and you may be advised to make some changes to your diet.

Radiotherapy can also cause inflammation of the bladder (cystitis). You may want to pass urine more often or you may have a burning feeling when you pass urine. Your doctor can prescribe medicines to reduce this. Make sure you drink plenty of fluids. These effects usually disappear gradually a few weeks after the treatment has finished.

A very small number of men may have difficulty passing urine and may need a urinary catheter put in. This is a tube that is placed inside the bladder to help the urine drain out of the body. Very rarely, some men may experience leakage or incontinence of urine.

Radiotherapy to your pelvis may make some of your pubic hair fall out. When you’ve finished your treatment, the hair will grow back. It may be thinner or finer than before.

External beam radiotherapy doesn’t make you radioactive. It’s perfectly safe for you to be around other people, including children, throughout your treatment.

We have information about understanding radiotherapy, which gives more information about this treatment and its side effects.

‘I walked my dog a few times a day for 15–20 minutes. The combination of exercise, fresh air and seeing the world around me started what became a fast recovery.’ Paul


Possible long-term side effects

Some men may have side effects that don’t improve. Others may develop side effects many months or years after radiotherapy finishes. These are known as long-term or late effects.

Erection problems

Radiotherapy for prostate cancer can cause the inability to have an erection (erectile dysfunction). Whether you develop erection problems or not will depend on your age and whether you are being treated with hormonal therapy as well. Erection problems may not happen straight after treatment. They sometimes develop over a period of 2–5 years afterwards. Ask your oncologist if they can give you an idea of your likely risk of ED

There are various treatments that can help if you develop ED.

We have more information on managing the late effects of pelvic radiotherapy in men, which tells you more about these effects and what can help.


Radiotherapy to the prostate can also cause permanent infertility. Some men find this very difficult to cope with. If you still want to father children naturally, you may be able to store sperm before treatment starts.

Bowel or bladder problems

Some men may have bowel or bladder changes as a result of radiotherapy. The blood vessels in your bowel and bladder can become more fragile. This causes blood to appear in your urine or bowel motions. It can take many months or years to occur and can sometimes be a long-term effect. If you notice any bleeding, tell your doctor so that they can arrange tests and treatment if necessary.

Occasionally, your bowel movements may be more urgent after radiotherapy. Some men suffer from excessive wind. Very rarely men have difficulty controlling their bowels (faecal incontinence). Tell your healthcare team if this happens. Although it may feel embarrassing to talk about, they can give you practical advice.

Often, radiotherapy can help improve problems with passing urine. But for a small number of men, it can lead to leakage of urine (urinary incontinence). This is due to damage to the nerves that control the bladder muscles. It’s unlikely to happen unless you’ve had an operation to remove part of the prostate gland (a transurethral resection of the prostate), or a prostatectomy, as well as radiotherapy treatment.

If this side effect occurs, tell your doctor. They can arrange for you to see a specialist continence nurse. You may also find it helpful to contact the Bladder and Bowel Foundation.


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

Back to Radiotherapy explained

Who might I meet?

You will meet many different specialists before, during and after radiotherapy treatment.