A fundraising drive to send Caoimhe Neeson, 3, for proton therapy, a targeted form of radiotherapy, has reached £20,000.
Initially, Caoimhe, of Sandyhills, Glasgow, was turned down for NHS funding for the £250,000 treatment, but after her case was re- assessed, the Proton Therapy UK Panel gave its approval.
The family is expected to fly to Jacksonville, Florida, this month for the treatment.
However, they are still battling to raise enough money for the family, including brother Corrie, 11, to travel and stay there for three months while Caoimhe has her treatment.
Hundreds of people across the Central Belt have rallied round to help through an online fundraising page.
Caoimhe was diagnosed with a fast-growing brain tumour three months after becoming unwell last year.
Doctors told mum Joe-Anne there was a only a 40% chance she would survive to her fifth birthday.
Surgeons operated soon after she was diagnosed but were unable to remove all of the tumour, because of its size and location.
Doctors have been amazed at her recovery from the operation after she regained her mobility and speech.
The youngster has been receiving chemotherapy at Glasgow's Sick Kids' Hospital, which has stabilised the cancer but it is probable it will return.
Proton therapy delivers a more precise dose of radiation without killing healthy tissue surrounding the tumour and is particularly beneficial for children who are still growing. Conventional treatment can lead to deafness, reduced IQ and secondary cancers.
Almost 150 patients have been funded for treatment overseas.
Joe-Anne said: "Not every child can be saved, and that is the devastating realism, but statistically Caoimhe would have a better chance of survival with this treatment."