Planning your radiotherapy

The radiotherapy team plans your external beam radiotherapy before you start treatment. This means working out the dose of radiotherapy you need and exactly where you need it. Your planning appointment takes from 15 minutes to 2 hours.

You usually have a planning CT scan in the radiotherapy department.

The scan shows the cancer and the area around it. You might have other types of scans or x-rays to help your treatment team plan your radiotherapy. The plan they create is just for you.

Photo of a CT scanner

Before your planning starts, your radiographer asks you to sign a consent form. If you're a woman they check with you that you’re not pregnant and remind you not to get pregnant during treatment. This is because radiation can damage an unborn baby.

Your planning appointment

Having a full bladder

You might need to have a full bladder for your planning scan. This is because having a full or partially filled bladder can help to reduce the dose to normal, healthy tissues near to the cancer. Your radiographers explain this to you when you arrive.

If you have a full bladder for your planning scan, you'll have to do this for all of your radiotherapy treatments.

Injection of dye

You might need an injection of contrast. This is a dye that helps body tissues show up more clearly on the scan.

Before you have the contrast, the radiographer asks you about any medical conditions or allergies. Some people are allergic to the contrast.

The scan

You lie on the scanner couch. You might lie on your front with a special cushion under you. Or on your back. 

Your radiographers (sometimes called radiotherapists) tell you if you need to remove any clothes. They need to see the treatment area, but cover you up as much as possible.

Your radiographers might put a thin metal wire or small metal ball into the anal margin. This is so the area clearly shows up on scans. Your doctor uses these scans to work out exactly where to give the treatment.

Once you are in position the radiographers move the couch up and through the scanner. You need to lie very still. The radiographers leave the room and the scan starts. It takes about 5 minutes. You won't feel anything. The radiographers watch from the room next door. 

You might also have other scans such as MRI scans or PET scans to help plan your treatment. 

Ink and tattoo marks

The radiographers make pin point sized tattoo marks on your skin. They use these marks to line you up into the same position every day. The tattoos make sure they treat exactly the same area for all of your treatments. They may also draw marks around the tattoos with a permanent ink pen, so that they are clear to see when the lights are low.

Photograph of radiotherapy tattoo marks

The radiotherapy staff tell you how to look after the markings. The pen marks might start to rub off in time, but the tattoos won’t. Tell your radiographer if that happens. Don't try to redraw them yourself. 

After your planning session

You might have to wait a few days or up to 3 weeks before you start treatment.

During this time the physicists and your radiographer doctor (clinical oncologist) decide the final details of your radiotherapy plan. They make sure that the area of the cancer will receive a high dose and nearby areas receive a low dose. This reduces the side effects you might get during and after treatment. 

Last reviewed: 
29 Apr 2019
  • Anal cancer: ESMO-ESSO-ESTRO Clinical Practice Guidelines for diagnosis, treatment and follow-up
    R. Glynne-Jones and others
    Annals of Oncology 2014. Volume 25, iii10-iii20

  • Neoplasms of anal canal and perianal skin
    D. Leonard and others
    Clinical Colon Rectal Surgery, 2011. Volume 24, Pages 54-63

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