UTV Live Tonight joined Oscar, his mum, dad and little sister Izzie, as they began their journey to Philadelphia for tests to see if he is eligible to receive new treatment.

The four-year-old from Belfast suffers from stage four neuroblastoma - an aggressive childhood cancer which could kill him.

The disease causes tumours to develop, in the stomach, spine, chest and neck, but can also spread to other parts of the body.

"Immunotherapy is great in the fight against neuroblastoma," his father Stephen explained.

"He was initially due to get it on his treatment on the NHS, as part of a clinical trial but he had to come off that clinical trial to go to London for additional treatment.

"So the only way we can be sure of getting him it was to launch the big fundraising campaign, raise the cash and go abroad and get it. Research suggests it will give him an extra 25% chance of survival which is great."

Almost 2wks of scans/tests/analysis begin this morning to ensure I qualify for the immunotherapy trial here. Fingers crossed! #TeamOscarUSA

— Oscar Knox (@Wee_Oscar) October 8, 2012

Little Oscar was diagnosed last year after he was taken to hospital as he had a sore shoulder.

"The outlook was grim," Stephen said. "It blew our whole world wide open."

"He's been through hell the amount of chemotherapy drugs and radiation therapy that he's been through in the last eleven months."

Stephen says he believes the therapy could save his life as it will reduce the risk of the cancer coming back.

"We just want him to have a chance at life, to grow up," he said.

"We could sit back here at home and cross our fingers, and hope to never see it again but that's not what we want to do."

"It's been really really tough on him and he doesn't understand and we don't have any answers," his mum Leona said.

"But he's managed to get through it so well. He's almost showing us how to do it."

He talks all the time about what he wants to be when he grows up, he wants to be a chef, an ambulance driver, a fireman - it changes everyday and when he says that, we can't help but think, is this going to happen? We want that to become a reality for us and for him to fulfil those dreams.

Leona Knox

She said she is nervous about getting Oscar on to the trial.

"We're going into the unknown here, we just don't know what's going to happen," she said.

"We hope Oscar gets through this consultation period and can get accepted on to the trial to get this treatment. Even if he does, we don't know what it holds for him, there's quite a lot of side effects with immunotherapy.

"If it doesn't happen, it will be back to the drawing board- we can't give up."

The family reached their goal of raising £250,000 to take Oscar to America for the treatment, with help from a social media campaign which went global.

The campaign was started earlier this year and Oscar now has over 15,000 Twitter followers, including many famous faces such as Belfast boxer Paddy Barnes, Snow Patrol frontman Gary Lightbody, Celtic star Joe Ledley and others.