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Petr David Josek, Associated Press
In this picture taken on Thursday, Sept. 11, 2014,11-years old Miki Roth displays a mask used during his proton beam therapy in Prague, Czech Republic. Miki Roth suffered from the same life threatening brain tumor and received similar proton treatment that 5-year old British boy Ashya King is set to start on Monday Sept. 15, 2014.

PRAGUE — British boy Ashya King underwent his first proton beam therapy session for a life-threatening brain tumor in Prague on Monday, a week after the 5-year-old boy was flown here from Spain.

Ashya's case caused an international uproar after his parents removed him from an English hospital last month without doctors' consent and police launched a manhunt to find him.

Ashya's parents, Brett and Naghmeh King, had fought a protracted battle to get him proton beam treatment, which targets tumors more directly than radiotherapy but isn't yet available for brain tumor patients in Britain.

An 11-year-old Czech boy who had the same disease as Ashya and was treated with proton beam therapy offered the British boy some advice.

"He can't say to himself: 'I'm ill, so I'm not going to do anything,'" Miki Roth told The Associated Press. "He should read or exercise, try to walk, exercise his legs with therapists that visit him."

Miki was diagnosed with medulloblastoma about two years ago. Following surgery, he received radiation therapy at Prague's Proton Therapy Center.

The treatment worked well for Miki, who was in a wheelchair when he arrived at the center for the first time. He walked on his own after 30 sessions, followed by a year of chemotherapy at Prague's Motol hospital.

Monday's treatment for Ashya was the first of 30 planned radiation sessions, the proton center said, combined with chemotherapy to be applied at Motol where he was admitted last week.

Spanish police arrested Ashya's parents on Aug. 30. The parents traveled to Spain to sell an apartment they owned there to raise funds for the Czech treatment privately. They spent a night in jail, but were released after British authorities canceled an arrest warrant.