Side effects of radiotherapy

The immediate side effects of radiotherapy are usually very mild. We discuss some of the general side effects here. Your child might have other side effects depending on the area of the body being treated. Your doctor or nurse will be able to explain these to you.


Your child may feel very tired while they are having radiotherapy and for a few weeks afterwards. Their energy levels may take a few months to return to normal once the treatment is finished.

Effects on the digestive system

You may find that your child loses their appetite. It may help for them to eat small snacks and meals frequently throughout the day, rather than large meals. Some children feel sick (nausea) or may be sick (vomit). Your child’s doctor can prescribe drugs to help with this.

Effects on the bone marrow

Radiotherapy to some parts of the body can sometimes affect the bone marrow, which produces the different types of blood cells. If this is likely to be a problem, your child will have regular blood tests during their treatment to check their blood cell levels. If these become low, they may feel very tired and lethargic. Let your child’s doctor know if this becomes a problem. Some children may need to have a blood transfusion – your child’s doctor can give you more information about this.

Effects on the skin

Some children develop a skin reaction similar to sunburn while having radiotherapy. This can happen after 3–4 weeks of treatment. In children with pale skin, the skin in the treatment area can become red and sore or itchy. In those with dark skin, it becomes darker. The extent of the reaction depends on the area being treated and your child’s skin type. Some children have no skin problems at all. Your child’s radiographers will be looking out for these reactions and will advise you about skincare.

Long-term side effects

Radiotherapy can sometimes cause other long-term side effects, which can develop gradually, months or sometimes years after the treatment. As time goes by, the effect of radiotherapy on any growing tissues may become more noticeable. In particular, radiotherapy to the brain can affect a child’s growth and development. Your doctor will be able to discuss this with you in more detail when planning treatment.

This information was written by the Children’s Cancer and Leukaemia Group (CCLG)