What does external beam radiotherapy involve?

You'll have your treatment at a hospital radiotherapy department. Before you start your treatment, you’ll see a health professional who specialises in treating cancer with radiotherapy. These can include a specialist doctor known as a clinical oncologist, or a consultant therapeutic radiographer who has had additional training and specialises in prostate radiotherapy. You may also see the cancer nurse at the hospital. They’ll talk to you about your treatment options, including side effects, and ask for your consent for your radiotherapy treatment.

Read more about what external beam radiotherapy is and who can have it as treatment here. You can also read about the short-term and long-term side effects of radiotherapy here. 

Before your treatment

Preparing for radiotherapy

You will need to prepare your bladder and bowel before the radiotherapy CT planning scan and before every radiotherapy treatment. The therapeutic radiographers ask you to do this because the prostate sits very close to your bladder, rectum and bowel.

The position of your prostate can change depending on how full your bladder and rectum are. If the size of the bladder and rectum change between your CT scan and treatment sessions, it could affect the accuracy of the treatment and increase the risk of side effects.

Your therapeutic radiographer may ask you to have a comfortably full bladder and empty rectum so that the radiotherapy is aimed at your prostate, while the surrounding areas receive as little radiation as possible.

Drinking fluids

Before you have your CT scan and radiotherapy treatment, you will need to be well hydrated. You should follow the advice from your radiotherapy team about how much fluid to drink before your planning CT scan and during your treatment. This could be water or diluted squash, or herbal decaffeinated teas such as peppermint.

Limit fruit juice, fizzy drinks or drinks that contain alcohol or caffeine (like tea or coffee), as these can give you wind or irritate the bladder and make you urinate (wee) more often.

Foods and diet

Some foods can make your rectum fill with gas or become larger. There are changes you can make to your diet to stop this.

• You may need to make some changes to your diet depending on how your bowel reacts during radiotherapy. Your radiotherapy team can advise you if changes are needed.

• Cut down food and drink that make you gassy. These include fizzy drinks, beans and pulses, spicy foods, and green leafy vegetables such as broccoli, cabbage and sprouts. Eating slowly and chewing your food well may also help reduce gas.

Every radiotherapy department does things slightly differently, so use this as a general guide. Your therapeutic radiographer will go through the preparation with you before you have your CT planning scan, and your first radiotherapy treatment.

If the preparation isn’t done properly, it can cause delays in your treatment. Speak to the radiotherapy team if you are unsure about any part of the preparation.

Radiotherapy planning session

You’ll have a CT scan two or three weeks before you start your treatment.

Before you have your scan, the therapeutic radiographers will ask you to complete the radiotherapy preparation (see above). Some hospitals will give you a micro-enema, which is a laxative that helps to empty your rectum. You may be asked to empty your bladder before your scan, and then drink some water. You'll then wait between 30 and 45 minutes for your bladder to fill up. Your radiotherapy team will explain this to you at your appointment.

You'll be taken into the CT scanner and lie down on the scanner couch. You may also have an injection of contrast dye. Your therapeutic radiographer will explain this fully if it’s applicable to you.

They will then take a scan that shows the cancer and area around it to plan your treatment.

After the scan, your therapeutic radiographer may make two or three very small permanent marks (tattoos) on your skin. These will help to get you into the same position when you go for each of your treatments. It will feel like a pin prick, and the tattoos will be the size of a freckle.

At some radiotherapy departments, you may have three or four gold seeds, called fiducial markers, put inside your prostate. These are about the size of a grain of rice. An ultrasound probe is put into your rectum to see your prostate. Hollow needles are then put into your prostate through your perineum (the area of skin between your scrotum and anus). The seeds are then passed through to your prostate. The seeds show up on X-ray images and help the therapeutic radiographer see the exact position of the prostate during each session.

Some men find having scans and treatments stressful. If you are anxious about these, speak to your doctor or therapeutic radiographer. They will take the time to go through ways that will help you cope. They may be able to help by playing relaxing music in the room or talking to you during your scan or treatment to keep you distracted. Or you may be able to have medication to help you relax.

It might also help to wear clothing and shoes that are easy to take off and put on, such as slip-on shoes and trousers with an elastic waist, as you will have to do this for your CT planning scan and treatment sessions.

During your treatment

You will usually have one treatment (known as a session or fraction) at the hospital five days a week, with a rest over the weekend. You can go home after each treatment.

If you have localised prostate cancer, the course of radiotherapy usually involves 20 treatment sessions over four weeks. You might hear this called hypo-fractionated radiotherapy.

At some hospitals, you may have a longer course of radiotherapy over seven or eight weeks instead. If you have a longer course, you’ll receive a slightly larger overall dose of radiotherapy – but the dose you receive at each session will be lower than if you have 20 sessions.

Studies have shown that having fewer treatment sessions over four weeks works just as well for men with localised prostate cancer as having more sessions over a longer time. The risk of side effects is also similar, and men usually find a shorter course of radiotherapy more convenient, as it involves fewer hospital visits.

If you were offered SABR, you will have as few as five sessions spread over one or two weeks.

You will have to follow the bladder and bowel preparation before each treatment session. Your therapeautic radiographer will explain the treatment process and your radiotherapy preparation instructions.

Getting into position

Once you are ready, your therapeutic radiographer will help you get into the exact same position as you were in at your planning scan. They may use the permanent marks made on your body during the CT scan. Some hospitals use other positioning systems instead of tattoos. This helps make sure that the radiotherapy treatment targets the same area each time.

You’ll need to keep very still while they get you in position. The therapeutic radiographers will then leave the room to give you the treatment. They can see you all the time and can come into the room if you need them.

Having the treatment

The therapeutic radiographers will first take a scan or X-rays to make sure the whole treatment area is covered, and that the radiotherapy targets the same area as in your planning scan.

The treatment then starts, and the machine may move around your body. It doesn’t touch you and you won’t feel or see anything. The machine may make a buzzing sound as it works.

You’ll need to keep very still, but the treatment only takes around 10 minutes, including the time it takes to get you into position.

You may also hear about image-guided radiotherapy (IGRT). This is used as part of all radiotherapy treatments. Taking images of the treatment area before each treatment allows your therapeutic radiographer to make small changes to the area that is treated, in case the prostate has moved slightly since your last treatment session. This makes sure the surrounding healthy tissue gets as little radiation as possible. IGRT also makes sure the whole treatment area is treated.

It’s safe for you to be around other people, including children and pregnant women, during your course of radiotherapy. The radiation doesn’t stay in your body, so you won’t give off any radiation.

Radiotherapy affects each person differently, but most people are able to carry on with their normal day-to-day activities. You may be fine to continue to work while having radiotherapy, or you may find it tiring and need time off work.

What happens after radiotherapy?

After you’ve finished your radiotherapy, you will have regular check-ups to monitor your progress. This is often called follow-up. The aim is to:

• check how your cancer has responded to treatment

• help you deal with any side effects of treatment

• give you a chance to raise any concerns or ask any questions.

Your follow-up appointments will usually start two or three months after treatment.

Before your follow-up appointment you will usually need a PSA blood test. You will then have PSA tests at least every six months in the first two years.

After two years, you may have follow-up appointments less often. Each hospital will do things slightly differently, so ask your doctor or nurse for more details about how often you will have follow-up appointments.

PSA blood test

The PSA test is a blood test that measures the amount of a protein called prostate specific antigen (PSA) in your blood. You will usually have a PSA test a week or two before each follow-up appointment, so the results are available at your check-up. This can often be done at your GP surgery. PSA tests are a very effective way of checking how well your treatment has worked.

After treatment, your PSA level should start to drop. Your PSA level won’t fall to zero as your healthy prostate cells will continue to produce some PSA. Every man is different, and your medical team will monitor your PSA level closely.

How quickly your PSA level drops, and how low it falls, will depend on whether you had hormone therapy at the same time as radiotherapy. If you had radiotherapy on its own, it may take 18 months to two years for your PSA level to fall to its lowest level (nadir).

Your PSA level may rise after your treatment is finished, and then fall again. This is called ‘PSA bounce’.

It could happen up to three years after treatment. It is normal, and doesn’t mean your cancer has come back or that you need more treatment.

If your PSA level consistently rises, particularly in a short amount of time, this could be a sign that your cancer has come back. If this happens, your doctor will talk to you about further tests and treatment options if you need them.

Treatment options after radiotherapy

If your cancer does come back, there are further treatments available. You may be offered hormone therapy to control your cancer, or you may be offered another treatment that aims to get rid of your cancer.

Treatments that aim to get rid of cancer that has come back are called salvage treatments.

After radiotherapy, these may include:

• surgery

• permanent seed brachytherapy or high dose-rate brachytherapy

• hormone therapy

• more external beam radiotherapy

• high-intensity focused ultrasound (HIFU) or cryotherapy, but these are less common and available only as part of a clinical trial.

There is no standard or best treatment after radiotherapy – your treatment options will depend on you and your cancer. For example, surgery can be difficult after radiotherapy because radiotherapy changes the prostate tissue and makes it harder for a surgeon to remove the prostate.

You may be more likely to get side effects if you have a second treatment. More research is also needed to look at how well treatments after radiotherapy work in the long term. Read more about what happens if your prostate cancer comes back.

Looking after yourself after radiotherapy

At some hospitals, you may have fewer follow-up appointments after your treatment and be encouraged to take greater control of your own health and wellbeing. You might hear this called supported self-management.

Instead of having regular appointments at the hospital, you may talk to your doctor or nurse over the telephone. You’ll still have regular PSA blood tests to check how your cancer has responded to treatment. But your GP may give you the results over the phone or in a letter. Some men prefer this type of follow-up, as it means you can avoid going to hospital appointments when you’re feeling well and don’t have any concerns.

Your doctor, nurse or therapeutic radiographer will give you information about the possible side effects of your treatment and any symptoms to look out for, as well as details of who to call if you notice any changes.

You, or your doctor or nurse, can arrange an appointment at any point if you have any questions or concerns.

References and reviewers

Updated: March 2026  | Due for Review: March 2029