Zac Oliver, 4, from Broseley, Shropshire, was diagnosed with rare blood cancer strains called Haploid. It is considered that the only child in Britain with this special radiation.
The family and supporters helped raise money in just two months, enabling him to travel to Philadelphia for treatment.
More than 100 trucks were involved in a convoy in Shropshire to raise money.
He and his family have now landed in America.
The four-year-old was chemotherapy and treatment at Telford's Princess Royal hospitals and children's hospitals in Birmingham.
On the flight that went to the country, Zac's mother Hannah cried and said:
"These are the tears of joy, that we did it! We are on the plane. I just want to say thank you to everyone. You want us luck."
Zac will receive a new treatment at the Childrens Hospital in Philadelphia.