A graphic illustrating proton beam therapy
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What access to proton beam therapy do UK patients have?

1 September 2014 Last updated at 18:35 BST

Dr Yen-Ching Chang, the lead on proton beam therapy at University College London Hospital, has told the BBC she believes UK patients with the highest needs probably have one of the most comprehensive levels of access to proton beam therapy in Europe.

University College London hospital is currently one of two hospitals in the UK developing a proton beam therapy centre.

The parents of Ashya King, who took him abroad for the treatment, are being held in police custody after they refused to consent to their extradition to the UK.

An international search was launched after the couple took the five-year-old, who has a brain tumour, from hospital in Southampton on Thursday.