Bowel cancer or colorectal cancer: Understanding side effects of radiotherapy
Radiotherapy for bowel cancer can cause side effects.
These can happen during treatment, soon after, or much later after treatment has finished. Early (sometimes called acute) side effects happen during and soon after radiotherapy. Everyone is different so it is not possible to say exactly when side effects will start, end, or how severe they will be. The best advice is to talk to your team if you are concerned about anything at all.
You might have side effects or symptoms not listed here, because everyone and every treatment is different. They may also be caused by a different part of your cancer treatment. Research and support for side effects and late effects of radiotherapy is growing.
Joining a support group can be a positive way to share your experiences, feel less alone, and come to terms with the physical and emotional impact of treatment. Ask your treatment or clinical team if you need more support or have any side effects at all.
- Key Information: Your reproductive organs (listed below) may be in or near the treatment area. Be sure to ask your consultant if this affects you. If it does, it’s important to discuss any plans or thoughts you have about having children as soon as possible. Your consultant can provide advice tailored to your situation. This can be a sensitive topic, and you may not have all the answers yet, but having the conversation early allows you to explore your options and make informed decisions.
- Reproductive organs include: ovaries, uterus, fallopian tubes, cervix, vagina, penis, testes, scrotum, prostate gland, urethra, and vas deferens.
This page looks at early side effects.
How likely am I to get early side effects?
Before treatment you will discuss and sign a consent form with your clinical oncologist or therapeutic radiographer. They will tell you what your chances are of getting early or late side effects.
You can click here to see different tumour site consent forms for radiotherapy. These consent forms are packed with useful information about early and late side effects.
When you consent to treatment, you are saying you understand that you have a chance of getting early and late side effects. Your team will use words like Expected, Common, Less Common and Rare.
This table shows what these words mean.
| Wording on the consent form | % chance of side or late effect | How many patients will get this? |
| Expected | 50 to 100% | Between half and all patients |
| Common | 10 to 50% | Up to half of all patients |
| Less common | Less than 10% | Fewer than one in ten patients |
| Rare | Less than 1% | Fewer than one in 100 patients |
Early side effects (during or soon after treatment)
Early side effects (during or right after treatment) Start during radiotherapy or shortly after completing radiotherapy and usually resolve within two to six months of finishing radiotherapy. But it is important to remember everyone is different.
a) General effects
- Feeling very tired or fatigued: You might feel very tired during and after your treatment. It’s important to get plenty of rest but sometimes you will still feel really tired, even with lots of sleep. Some tiredness can be caused by having cancer and having cancer treatment, and some can be caused by travelling to and from hospital every day for treatment.
- Skin reactions: You might notice a change in colour, swelling, itching, or changes in the texture of your skin where you’re treated. For people with lighter skin tones these changes can be pink, red or darker than the surrounding area. People with brown and black skin tones might have colour changes such as maroon, purple, yellow or grey pigment changes. Or the skin can look darker than the surrounding area. These changes usually improve after treatment, but this can take 4 to 6 weeks in some cases.
- Hair loss: you might lose hair in the area where you are treated. Often, this grows back over time.
- Sickness: You may feel sick or be sick, but this is rare.
- Sexual changes: Soreness and tenderness caused by treatment can make it difficult to have penetrative sex. Treatment can sometimes effect your ability to have an erection.
b) Effects on the bladder
- A common side effect is the need to go to the toilet more often (frequency) and not being able to hold it (urgency). You may also feel a stinging or burning when you wee (cystitis). Some days, this might feel worse, especially if you’re getting extra fluids with chemotherapy.
- Drinking lots of water can help make weeing less painful. There are medications that can be prescribed to help with any pain so talk to your treatment team.
c) Effects on the bowels:
- It is common to get more wind or loose, watery poo, or you may notice a change in how your bowels work.
- A common side effect is needing to poo more often (frequency) or not being able to control it (urgency).
- It is common to experience some pain in the area where you are treated.
- These problems usually get better a few weeks after the treatment ends.
What can help with these early side effects?
Here are some ideas you can try.
- Resting: Get lots of sleep and take breaks if you feel tired.
- Keeping active: Gentle movement can help you feel better, both during and after treatment. Your treatment team can tell you what is safe for you to do.
- Managing Bowel Problems: Professional advice on what food and drink you can have can help. You can also take medicine to help with diarrhea and any sickness. Tell your treatment team of any changes.
- Coping with bladder problems: Drink plenty of water and tell your doctor or treatment team if it hurts when you wee. Medicines can be prescribed to help.
- Skin reactions: Your treatment team can suggest creams to soothe your skin. Sometimes, extra care is needed if the skin breaks down in the treatment area. Wear loose clothing and stay out of the sun. Talk to your team about washing, shaving and caring for your skin in your treatment area. You might have to change your normal routine during treatment and for a short time after, especially if you develop a radiation skin reaction.
- Drinking fluids: Drinking plenty of fluids such as water, juice and squash can help with fatigue and tiredness caused by your treatment. It can also help flush out toxins in your body caused by treatment. You can try diluted juice if you don’t like water.
- Tell your treatment team: Always let your treatment team know if you have any side effects. They are there to help you.
- Supportive measures: Your doctors might suggest things you can do to feel more comfortable, like resting more, eating certain foods, or using creams on your skin.
- Medications: If you have symptoms like nausea, pain, or skin reactions, your team can prescribe you medicines to help make these better.
- Alcohol use: Please follow the NHS guidelines on safe drinking levels and any instructions you get from your team on what is right for you, your diagnosis and your treatment. If in doubt, please ask your team.
- Sexual changes: Talk to your team if you are having issues and they can offer advice.
Click here to learn more about late effects.
Further information
Learn more about side effects and support here:
https://www.bowelcanceruk.org.uk/how-we-can-help/
Women’s Health Concern | Confidential Advice, Reassurance and Education (womens-health-concern.org)
Pelvic Radiation Disease Association
Learn more about radiotherapy consent forms here:
https://www.rcr.ac.uk/our-services/management-service-delivery/national-radiotherapy-consent-forms/
Learn more about radiation skin reactions here:
Learn more about managing cancer fatigue:
Managing and treating cancer fatigue | Cancer Research UK
Cancer-related fatigue | NHS inform
Advice on alcohol use:
Drink less – Better Health – NHS (www.nhs.uk)
Learn more about LGBTIQ+ support around cancer treatment and sex:
