Why proton therapy

A more precise way to treat cancer

Radiotherapy is one of the most important tools in cancer care. Around half of all cancer patients need it at some point, and proton therapy delivers radiation treatment with far greater precision than conventional X-rays.

The difference

Radiation that knows where to stop

Conventional radiation, delivered as X-rays, does not stop at the tumour. It passes through the body, depositing dose in the healthy tissue and organs in front of and behind its target. For many patients that trade-off is manageable. For others, especially children and patients with tumours near the brain, spine, eyes or other critical organs, the damage to healthy tissue and nearby organs carries a lasting cost.

Proton therapy is different. It is widely recognised as superior to conventional radiotherapy in cases where sparing healthy tissue matters most, and where using protons makes the clinical difference.

The science

How it works: the dose stops where the cancer is

Protons are drawn from the nuclei of hydrogen atoms. Hydrogen is heated and separated into electrons and protons. These protons are then accelerated in a machine called a cyclotron to around two-thirds the speed of light. Magnetic guidance systems steer the proton beam through an evacuated path and focus it precisely onto the tumour.

Protons are drawn from the nuclei of hydrogen atoms. When hydrogen is heated it separates into electrons and protons, and those protons are then accelerated, in a device called a cyclotron, to around two-thirds the speed of light. Magnetic guidance systems steer the beam through an evacuated path and focus it precisely onto the tumour.

As protons travel through tissue they release very little energy, until, just before they come to rest, they deposit the bulk of the dose in a narrow band called the Bragg peak, and then stop. Conventional X-rays carry an exit dose that continues into the healthy tissue and organs beyond the target. Protons leave no exit dose.

Radiation dose Depth into the body TUMOUR Conventional X-rays exit dose continues Proton beam Bragg peak

FIGURE: Bragg-peak depth-dose diagram, comparing the proton beam (energy released at the tumour, then nothing) with conventional X-rays (dose all along the path plus exit dose).

By tuning the energy of the beam and narrowing it to a “pencil” less than a millimetre across, clinicians deliver the dose exactly within the boundaries of a tumour. Advanced treatment planning builds underpins this in three dimensions, allowing the dose to be “painted” across the tumour layer by layer, adjusting for the exact shape and position of each patient’s cancer

  • Protons accelerated to ~⅔ the speed of light
  • “Pencil” beam less than 1 mm across
  • Energy tuned to reach an exact depth
  • Three-dimensional, layer-by-layer delivery

The stakes

Why it matters most for children

Roughly a third of children with cancer need radiotherapy. A child cured today may live another seventy years, and the healthy tissue spared during treatment still has a lifetime of growing to do. That is why proton therapy is so valuable in paediatric care: it limits the lifelong late effects of radiation.

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Growth abnormalities

Radiation to developing bone and tissue can permanently alter how a child grows.

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Neurocognitive impairment

Damage to healthy brain tissue can affect a child’s learning and development for life.

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Endocrine dysfunction

Hormonal systems can be disrupted by radiation exposure in childhood.

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Secondary cancers

A second, radiation-induced cancer can emerge, sometimes decades after the first was cured.

Every child treated with proton therapy instead of conventional radiation has a better chance at a full life afterward.

Adults too

It matters for adults too

This is not only a treatment for paediatrics and young people. Between 50 and 60% of adult cancer patients need radiotherapy, and for many, those with tumours close to the brain stem, spinal cord, heart or other sensitive structures, the precision of proton therapy can mean fewer side effects, a better quality of life during and after treatment, and a lower risk of long-term complications. More conventional cancers such as those of the prostate are highly suitable for very effective treatment with protons.

The need

The scale of the need in South Africa

~120,000South Africans diagnosed with cancer each year
~120,000South Africans who die of cancer each year 
50–60%Of adults with cancer need radiotherapy
⅓Of children with cancer need radiotherapy

The gap

World-class treatment, out of reach

There are around 150 proton therapy centres in operation around the world. As the map shows, they cluster in the global north. Not one is in sub-Saharan Africa. For families in our region, reaching this treatment today means the cost and upheaval of travelling abroad, an option open to very few. South Africa once led this field. UCT is bringing that capability home.

Global proton therapy centresEqual Earth map showing 65 facilities over countries shaded by prototype income classification.

FIGURE: World map of proton therapy centres. Blue dots mark operational centres (clustered in North America, Europe and East Asia); a coral dot marks the planned UCT centre in Cape Town.

 

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