Proton therapy for children — how it differs

How conventional radiation works

Standard radiation therapy delivers X-ray beams — streams of photon energy — into the body. As a photon beam travels through tissue, it deposits energy all along its path: entering through the skin, passing through the tumour, and continuing to deposit some energy in the healthy tissue beyond. Modern conventional radiotherapy has become very sophisticated at shaping beams from multiple angles to concentrate the dose at the tumour and reduce the exit dose — but some radiation to surrounding healthy tissue remains unavoidable.

How proton therapy is different — the Bragg peak

Proton beam therapy works on a different physical principle. When protons enter the body, they travel through tissue while losing energy slowly — then release the majority of their energy at a very specific depth called the Bragg peak. The radiation oncologist and treatment physicist calculate and control this depth precisely so it coincides with the tumour. Beyond the Bragg peak, the proton beam essentially stops. The result: the tumour receives its full planned dose, while the tissue immediately behind the tumour receives very little.

This does not mean no healthy tissue is exposed to protons at all — the beam still has to pass through the tissue between the skin surface and the tumour. But the difference lies in what happens on the other side. For a tumour located near a critical structure — the spinal cord, brain stem, optic nerve, or a developing growth plate — this exit-dose reduction can be clinically meaningful.

Why healthy tissue sparing matters more in children

Children's bodies are still growing. Radiation reaching developing bone can affect how that bone grows — a small dose to the spine during treatment can cause uneven vertebral development and height differences over the following years. Radiation reaching the developing brain — especially in children under five — can affect the way cognitive abilities develop. Radiation to the heart or lungs during treatment for chest tumours carries a risk of cardiac and pulmonary effects that may not appear for ten or twenty years but are real and documented. This is the core reason why the proton vs radiation discussion is more clinically significant for children than for older adults: a child treated at five years old has potentially seven decades of life ahead. The goal is not just to control the cancer — it is to give the child the best possible long-term health after treatment ends.

For many childhood cancers and many tumour locations, conventional radiotherapy remains highly effective and the standard of care. Proton beam therapy is not automatically superior for every child — it is a tool that is particularly valuable in specific situations where the tumour's location makes reducing the exit dose medically important. Your child's radiation oncologist can compare the planned dose distributions for both options, which makes it possible to have a clear, evidence-grounded conversation about whether proton therapy offers a meaningful advantage in your child's specific case.

Treatment planning comes first

Before any proton therapy begins, the team creates a detailed treatment plan. This involves a planning CT scan — sometimes with an MRI as well — to map the tumour and the surrounding structures in three dimensions. The radiation physicist and the oncologist use this map to calculate precisely where the Bragg peak should fall and how many beams from which angles will deliver the planned dose to the tumour while keeping doses to critical structures within safe limits. For children, the planning process also includes a comparison of the proton dose plan with an equivalent photon plan, so the team can demonstrate quantitatively what difference the proton approach makes for that specific child's anatomy.

Immobilisation and sedation for young children

Proton therapy is only effective if the child is completely still while the beam is being delivered. For older children and teenagers, this is achieved with a custom-fitted immobilisation device — a mould or mask made specifically for your child's body position. For very young children — typically under five — who cannot be expected to lie still reliably for the duration of a treatment session, daily general anaesthesia or sedation is usually required. While this adds complexity, paediatric anaesthesia teams experienced in radiation oncology manage this routinely. The anaesthesia is short and light, and most children recover quickly. The proton therapy team plans the immobilisation approach during the pre-treatment phase and discusses it with parents before treatment begins.

Daily treatment sessions and total duration

Proton therapy is typically delivered as a course of daily sessions — called fractions — five days a week, with weekends off for recovery. The total number of fractions depends on the cancer type, the dose needed, and the protocol being followed. Some courses run for four to six weeks; others are shorter. Each individual session is brief — the actual beam delivery takes only minutes, though set-up time and any anaesthesia preparation add to the total appointment length. Parents are encouraged to bring comfort items and ask questions at each visit. The radiation team and nursing staff are present throughout every session.

Side effects during treatment

The immediate side effects your child experiences during proton therapy are related to the area being treated, not to the type of radiation particle used. Fatigue is common across all forms of radiation. Skin changes, hair loss, nausea, or mucositis (mouth soreness) depend on the treatment site. The advantage of proton therapy over conventional radiation is expected mainly in reducing late effects — those that appear months or years after treatment ends — rather than in making the immediate treatment experience significantly easier. Your radiation oncologist will discuss what immediate side effects to watch for based on where your child's tumour is being treated and what the management plan for those side effects looks like.