Proton beam centres 'to treat 1,500 patients a year'
Two new NHS proton beam therapy facilities could offer treatment to 1,500 cancer patients a year when they open in the next few years.
The therapy - which is particularly helpful for children with rare and complex tumours - was highlighted with the case of Ashya King last year.
The five-year old's parents took him abroad after doctors in the UK did not recommend it for his brain tumour.
Experts say the new centres will be "game-changing".
The therapy allows precise targeting of certain tumours, increasing the success rates and reducing the risk of damage to surrounding tissues.
But it is not yet available in the UK - apart from one clinic to treat eye conditions.
On Wednesday, a ceremony at University College London Hospital (UCLH) - attended by Health Secretary Jeremy Hunt - marked the start of construction at one of the sites, due to open in 2019.
The other, at the Christie cancer centre in Manchester, will start taking patients in 2018.
Separately, in May this year the private company Proton Partners International said it had plans to open a centre in Newport in south Wales.
This clinic would do some NHS work.
Experts say the opening of NHS facilities in London and Manchester will allow them to provide the specialist treatment to a wider selection of patients than any other healthcare system in Europe.
Sir Robert Naylor, chief executive of UCLH, added: "To have work under way on this long-awaited centre is tremendous news.
"This will be a game-changer for NHS patients who will benefit from local access to advanced treatments."
Currently about 120-140 patients a year have to go to foreign clinics for treatment funded by the NHS.
Four-year-old Keeva Hanbury from Hertfordshire and her parents joined health leaders at the launch at UCLH.
They had to travel to the United States for treatment including proton beam therapy after she was diagnosed with a rare cancer.
Although the treatment went well the family described it as a "massive" upheaval.
Currently the average cost to the NHS of proton beam therapy for each patient sent to foreign clinics is about £75,000.
This includes travel and accommodation and associated medical care while abroad such as chemotherapy.
But the cost will be nearly half as much when the new proton beam centres in the UK open, at approximately £40,000 per patient.
Building centres to house the machines will be no easy task.
Targeting protons at a tumour requires a machine called a cyclotron, weighing about the same as a jumbo jet.
The new building at UCLH will house a blood cancer treatment facility and a new short-stay surgery unit as well as the proton beam therapy centre.