Proton beam therapy

If your child has certain types of cancer, your specialist may recommend they travel abroad to have a specialised form of radiotherapy called proton beam therapy.

What is proton beam therapy?

Proton beam therapy is a type of radiotherapy. Conventional radiotherapy usually uses high-energy X-rays (also called photons) to destroy cancer cells, but proton beam therapy uses small parts of atoms called protons instead. Protons, however, can more precisely target a tumour than x-rays can. The protons release their energy at the site of the tumour. Proton therapy is currently unavailable in the United Kingdom. The Department of Health will pay for proton treatment of carefully selected patients at hospitals in other countries, usually Switzerland and the USA, if this is felt to be the best treatment for them. Most children who need proton beam therapy are treated in the USA.

Although the evidence and follow-up data for proton beam therapy is still limited, the data gathered so far suggests it has good outcomes for certain forms of cancer, including complicated childhood cancers and may cause less long-term side effects. There is no difference in the biological effectiveness of protons versus photons in terms of the damage they cause to cancer cells, but they deliver the dose slightly differently.

How proton beam therapy works

Like other forms of radiotherapy, the aim of proton beam therapy is to destroy the DNA in cancer cells. DNA is the instruction code that tells a cell what kind of cell it is and what job it has to do. Destroying it kills the cancer cells and shrinks the tumour.

With proton therapy the protons’ energy hits mainly the tumour site and, unlike photons, does not deliver a dose beyond the tumour. This means the dose of radiation maps onto the tumour better and there is less damage to healthy tissue. Because of this, doctors may recommend proton therapy if a young person or child has a tumour that is close to delicate parts of the body, such as the brain or spinal cord.

The types of diagnoses in children up to 16 years that are referred for proton therapy are:

  • Brain tumours - craniopharyngiomas, ependymomas, optic pathway or low grade
  • Gliomas
  • Sarcomas - Ewings sarcoma, parameningeal rhabdomyosarcomas, pelvic sarcomas, rhabdomysosarcoma (orbital, head and neck and pelvic), spinal and paraspinal bone and soft tissue tumours, base of skull and spinal chordomas and base of skull chondrosarcoma
  • Retinoblastoma
  • Pineal parenchymal tumours

The types of young adult diagnoses that are referred for proton therapy are:

  • Base of skull and spinal chordoma
  • Base of skull chondrosarcoma
  • Spinal and paraspinal bone and soft tissue sarcoma (Non-Ewings)

How is proton beam therapy given?

People having proton beam therapy are treated as outpatients. Treatments are usually given daily from Monday to Friday with weekends off. The proton treatment course usually lasts about six to seven weeks in total. Because proton beam therapy is so carefully targeted, it is very important that people having it stay still during the treatment. If your child is having proton beam therapy on your head or neck, they may have a special mask made for them that keeps their head still.

For younger children, who are more likely to move around, staff at the therapy centre may use a special beanbag shaped to their body or straps to help them stay still. Younger children may also be given an anaesthetic to make them sleep.

Proton beam therapy is painless and treatments usually last about 1-1 1/2 hours in total.  If your child needs an anaesthetic, you may need to spend about 3-3 1/2 hours at the treatment centre to allow them time to recover.

June 2012, next planned review 2014.

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