Image copyright PA Image caption Mason is studying for his GCSEs

Fifteen-year-old Mason Kettley, who has a rare brain cancer, is about to become one of the first NHS UK patients to have proton-beam therapy, at a new dedicated treatment centre.

He is starting treatment at the £125m centre at Manchester's Christie hospital.

Previously, most patients needing the treatment had to travel abroad.

The specialist radiotherapy targets cancers without damaging tissues around the tumours.

This is good for children who are at risk of lasting damage to organs that are still growing but it is available in only a handful of countries around the world.

Image copyright PA Image caption Radiographers David Kirk and Melissa Bentley with a test dummy as they demonstrates the new proton-beam therapy centre at the Christie hospital, in Manchester

Mason, from Angmering, West Sussex, was diagnosed with a brain tumour in October.

"I had some headaches and stomach pains and usual things, and got check-ups at the doctors," he said. "My mum said, 'He's not gaining weight or growing.'"

An MRI scan showed he had a rare pilomyxoid astrocytoma brain tumour. It couldn't be operated on because of a risk of blindness and other "catastrophic" complications.

"The machine is intimidating because of its size," he said.

"It's a bit nerve-wracking but this is a better choice than chemo because it's more effective.

"Because of my age, [doctors] thought radiation would be a better choice."

What is proton-beam therapy ?

Patients have been able to travel overseas for NHS funded treatment since 2008. But some haven't been able to travel because they are too ill or their treatment need was too urgent.

The travel also caused major upheaval to families at a very stressful time.

Media playback is unsupported on your device Media caption What is proton-beam therapy?

The Christie hospital centre opened in autumn 2018. The first patient to have PBT there, who is still undergoing treatment, did not want publicity.

A second health service PBT centre is also set to open in the UK, at London's University College Hospital, offering the therapy from 2020.

It is hoped that each will each treat up to 750 patients every year.

The Clatterbridge Cancer Centre in Merseyside has been delivering low-energy proton therapy specifically for NHS patients with eye tumours.

But the two new centres will be the first to deliver higher doses to a broader range of cancers - including brain, head and neck cancers and sarcoma, a rare cancer of soft tissue.

Both will carry out research to assess PBT's suitability for treating other cancers.

Proton-beam therapy made headlines around the world in 2014, when the parents of five-year-old Ashya King were arrested after taking him abroad for the treatment in Prague.

Oncologist Gillian Whitfield is leading Mason's care. She said his was a low grade (slow growing) tumour with a "high chance of cure".

"For Mason, in comparison to conventional radiotherapy, PBT should carry a lower risk of some important long-term side-effects of treatment - particularly effects on short-term memory and learning ability - and the risk over the next eight decades of the radiation causing other tumours.

"This is particularly important for children and teenagers with curable tumours, who will survive decades after treatment and are at much greater risk of serious long-term effects of treatment than adults."

Mason, who lives with his mother, step-father, and four siblings, and is in the middle of preparing for his GCSEs, will have 28 treatment sessions taking place Monday to Friday for almost six weeks.

He has had a specially made radiotherapy mask created to keep his head perfectly still during the therapy. And while he may get short-term side effects such as vomiting and headaches, long-term side-effects are rare.

And he said his experiences as a patient had influenced his future career plans.

"I'm so grateful to all the doctors involved in my care and I'd love to do what they do one day - it will be my way of giving something back."