Brain tumour patient Ashya King has undergone his first proton beam treatment at a Czech clinic.
The five-year-old is receiving post-operative radiotherapy at the Proton Therapy Centre (PTC) in Prague.
Doctors treating the British boy, whose parents were briefly detained after taking him out of the country for specialised cancer treatment, said his first day of therapy went according to plan.
It was the first of 30 sessions.
He will be treated at the private clinic every day for the next six weeks.
He had previously undergone tests at the clinic, over the past week, since arriving from Spain.
Ashya's parents Brett and Naghemeh King, from Southsea, sparked a police hunt when they removed him from Southampton General Hospital on 28 August after disagreeing with doctors.
They wanted him to have proton beam therapy, which was not available to them on the NHS.
They were arrested in Spain and spent several days away from their son, reuniting once the Crown Prosecution Service withdrew the European arrest warrant.
The family was flown by private jet to Prague ahead of Ashya's treatment at the PTC.
The clinic said Ashya's first day of treatment went well with no surprises.
He was placed in a special plastic mould to keep him still, given a general anaesthetic and then his brain and spine were irradiated with protons.
A spokeswoman for the clinic told the BBC Ashya's spirits appeared to be lifting by the day.
She added he was smiling more than during his initial consultation last week.
The treatment is a type of radiation therapy that uses beams of protons - or small parts of atoms - rather than high energy X-rays, as with conventional radiotherapy.
The protons can be precisely directed at a tumour and, unlike conventional treatments, the beams stop once they hit the target, rather than carrying on through the body.
Ashya's attending doctor, radiation oncologist Dr Barbora Ondrova, said: "There is a 70 to 80% survival rate for the condition such as Ashya has and there is now every reason to hope that he will make a full recovery."
The first 13 sessions will focus on the brain and spine, to ensure the tumour he previously had removed at Southampton General Hospital has not spread, and the remaining 17 will aim at irradiating where the brain tumour once was.