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Proton beam therapy: What is it and how does it treat cancer?

Ashya is cured of cancer after 30 proton beam sessions, his parents say

By Steve Connor and Lamiat Sabin

Parents Naghmeh and Brett King sparked an international manhunt last August after they removed Ashya from Southampton General Hospital last August.

They took the boy to their holiday home in Marbella, Spain, where the parents were arrested and spent several nights in jail.

Ashya was finally allowed to undergo the proton beam treatment, instead of radiotherapy offered on the NHS, in the Czech capital Prague after a long High Court battle.

What is proton beam therapy?

This is a form of radiotherapy treatment for cancer involving high-energy protons, which are hydrogen atoms stripped of their electrons. Proton particles penetrate the skin and release much of their energy at the site of the tumour, destroying the capacity of cancer cells to replicate.

What is the difference with conventional radiotherapy?

Conventional “external beam” radiotherapy uses X-rays or gamma rays, which are essentially beams of photons rather than protons. The fast-moving and energetic photons work in the same way as protons by causing breaks in the DNA molecule of cancer cells, which inhibits their ability to replicate. However, the big difference between the two forms of radiotherapy is that protons release about 80 per cent of their energy directly within a tumour, whereas conventional radiotherapy releases energy continually to the healthy tissues on both sides of the tumour. 

What is the advantage of proton beam therapy?

It all comes down to a part of physics called the "Bragg Peak". A phenomenon of protons is that they can be “programmed” to stop at a specific distance within the body, which is where they will release most of the energy - the Bragg Peak. Conventional radiotherapy beams made of photons continue to release energy before and after passing through the tumour, thereby damaging the healthy tissues of the body and causing more, worse side-effects.

Read more: Ashya King 'cured' of cancer after family flees UK for proton therapy in Prague

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