Find out about different kinds of radiotherapy used to treat cancer, how it works, and the side effects you might experience.

  • Radiotherapy is a type of cancer treatment
  • It uses radiation to destroy cancer cells
  • It can be given to you internally or externally
  • It can be used before surgery to shrink a tumour first
  • There are some side effects from radiotherapy that are good to talk through with your clinical team before you start

What is radiotherapy?

Radiotherapy uses radiation to destroy cancer cells. You may have it as part of your cancer treatment, depending on the type of cancer you have and how advanced it is.

Radiotherapy does permanent damage to cancer cells – causing them to die or stop growing. Healthy cells nearby are also damaged, but these are usually able to repair themselves and get back to normal.

Radiotherapy can be given to you externally or internally.

In external radiotherapy, machines are used to target cancerous cells with special X-rays. In internal radiotherapy, radioactive liquids and implants are used inside your body to attack cancerous cells.

Whichever type you have, there’s a lot of jargon – photon beams, protons, particle beams, high-energy X-ray beams. So just keep asking for explanations if you’re ever confused.

Radiotherapy is used for lots of reasons. It can be used before surgery to shrink a tumour so it’s easier to remove, or after surgery to kill off any cancer cells that survived the surgery. Some cancers will just need radiotherapy, although this is rare in young people’s cancers.

And it can be used to help cancer symptoms in more advanced cancers.

External beam radiotherapy

During external beam radiotherapy, you’ll need to stay still for a few minutes while high-energy radiation is targeted at your cancer and a small area of surrounding healthy cells, in case the cancer has spread.

The machine that’s used doesn’t touch you, you won’t feel any pain and you usually won’t need to stay in hospital overnight.

There are other types of external radiotherapy too, which doctors use to target very specific areas. You’ll need to keep very still when having this type of treatment – your care team will help you with this, and talk you through everything you need to do.

Internal radiotherapy

Internal radiotherapy involves radioactive liquids and implants.

You might be given a liquid to drink, a tablet to swallow or an injection. This won’t cause any long-term harm, but you might need to stay in a hospital room by yourself for a few days while you become less radioactive.

Implants are things like wires and tubes, put in your body to release radiation near cancer cells, then left in your body for between a few minutes and a few days – or sometimes for good.

How long does radiotherapy treatment take?

If you have external beam radiotherapy, you’ll be given lots of individual treatments. These are called fractions.

People often have five treatments a week, one a day Monday to Friday, with a chance to rest over the weekend and to let healthy cells recover. You might need treatment over the weekend too, although this is rare. 

In total, external radiotherapy usually lasts between one and seven weeks.

If you have internal treatment, your doctors will let you know how long a radioactive implant will be left in for, or how often you need to visit hospital. You might need to stay in hospital after internal treatment.

What are the side effects of radiotherapy?

A lot of the common side effects of external radiotherapy are quite mild and don’t last too long, but they can still be unpleasant.

Side effects of external radiotherapy can be:

Sore skin

You might find your skin gets red or darker. It might get dry and itchy too, or peel like you’ve spent too long in the sun. This usually heals in a couple of weeks. In the meantime, use unperfumed soap and don’t shave any skin that hurts. If it’s summer, you should keep covered up, and wear some sun cream (factor 30 or higher) on any exposed skin. If it’s winter, protect your skin from chilly winds by wearing layers and a scarf.

Losing your hair

Your hair might fall out in the area you’re having treated. So if you’re having treatment on your head or neck, there’s a good chance you’ll lose the hair on your head, and this can be tough. Your hair may grow back a few weeks after treatment ends. Often it will grow back much thinner, and sometimes it doesn’t grow back at all. But this will just be where the radiotherapy has been directed – not all over. It’s worth asking the radiotherapy team about this before you start your treatment. 


Your body uses a lot of energy to repair healthy cells that are damaged by radiotherapy, so give yourself plenty of time to relax if you’re feeling wiped out. Ask friends to bring over films, magazines, video games or whatever you feel up to doing.


Most people aren’t sick during radiotherapy – it depends where the radiotherapy is being directed. It’s more likely if you’re having radiotherapy to your stomach or pelvis, but this usually stops a few days after your treatment. If you do feel rough, talk to your doctor, who will be able to give you some anti-nausea drugs. Diarrhoea can be a common problem too, and your doctor can also prescribe something to help with that.

Not feeling hungry

It’s not surprising, really – if you’re feeling sick and tired, eating’s never going to be the first thing on your mind. If you do find you’re not feeling hungry, try and keep your energy levels up by eating little and often.

And some more radiotherapy side effects…

Swallowing can hurt if you have radiotherapy to your throat. Your joints might become stiff where you’re being treated. And you might find you lose interest in sex. All of these are likely to get back to normal once your treatment ends.

Long-term effects

Sometimes, radiotherapy can have side effects that don’t get better once the treatment has finished. These vary depending on where your cancer is but, if you’re worried, talk to your doctor or nurse about possible long-term side effects before you start any treatment.

Questions to ask about radiotherapy

Cancer and cancer treatment can be confusing. So never be afraid to ask questions. And if you don’t understand the answers you get, keep asking until you do.

If your doctor recommends radiotherapy as a treatment for you, you might like to ask:

  • What kind of radiotherapy is being recommended?
  • Why is it the best option?
  • Will it be combined with other treatments?
  • How long treatment will last?
  • What the side effects might be, and how we can reduce them?
  • What are the possible long-term effects?
  • How effective is it likely to be?
  • Are there other options which might work?
Patient Information Forum - Trusted Information Creator

PIF TICK accredited information

The Patient Information Forum is the UK membership organisation and network for people working in health information and support. The PIF TICK is the UK-wide Quality Mark for Health Information.

Find out more