The case of Ashya King, the five-year-old cancer patient whose parents fled with the boy to Europe seeking specialist medical care, has demonstrated the desperate lengths some will go to in order to treat the seriously ill.
Ashya's father, Brett King, said the family were hoping to get to the Czech Republic, having been dismayed by attempts to treat his son on the NHS at Southampton General Hospital.
His parents, who have been taken into custody, had been seeking proton beam radiotherapy - currently only available to treat eye conditions on the NHS in the UK.
Countries throughout Europe, however, already use proton beam for a range of cancers in adults and children.
According to Cancer Research UK, the treatment differs from X-ray methods by aiming proton beams at cancers.
It works by sending charges into cancer cells, with doses of radiation aimed directly at the tumour. At the same time, the treatment spares healthy tissue, particularly tissues and organs behind the tumour.
The treatment is popular because it has a lower risk of side effects, though others are concerned that the long-term impact of the nascent procedure is not yet known.
The only proton beam facility in the UK is at the Clatterbridge Centre for Cancer NHS Foundation Trust in the Wirral, Merseyside, which delivers "low energy" therapy for rare cancers around the eye.
But NHS England said high energy facilities for the UK were in the process of procurement and, in 2018, proton beam therapy will be offered to up to 1,500 cancer patients at the Christie NHS Foundation Trust in Manchester and University College London Hospitals NHS Foundation Trust in London.
Patients can also access proton beam therapy abroad through NHS funding.
They must be assessed by a panel who may decide patients are not suitable if there will be no clinical benefit from the treatment, NHS England said.
Between 2008 and 2013, 412 NHS patients were approved for proton beam therapy abroad including 293 children, it added.
Patients and their families could be away from home for eight to 10 weeks during treatment. The average cost of treatment is £100,000 per patient, NHS England said.
In a video blog posted on YouTube prior to his arrest in Spain, Mr King said he was prepared to raise the money to pay for his son's treatment in Europe.
''Proton beam is so much better for children with brain cancer,'' he said. ''It zones in on the area, whereby normal radiation passes right through his head and comes out the other side and destroys everything in his head.
''We pleaded with them (in Southampton) for proton beam treatment. They looked at me straight in the face and said with his cancer - which is called medulloblastoma - it would have no benefit whatsoever.
''I went straight back to my room and looked it up and the American sites and French sites and Switzerland sites where they have proton beam said the opposite, it would be very beneficial for him.
''Then I spoke to them again, I wrote a letter which he never responded to, saying okay - I will sell my property in order to pay for the proton beam.''
A Department of Health spokeswoman said: "Decisions on treatment for individual patients are made by doctors who are best placed to know what their patient needs.
"We are investing £250 million in new proton beam therapy facilities, in Manchester and in London, and more people are being funded to go overseas until facilities are available in the UK."
The NHS will also fund a patient's travel and accommodation costs and some other expenses if they are approved for proton beam therapy abroad.