He's one of Australia's youngest patients to have Gamma Knife Surgery for his rare and potentially fatal condition - complex deep-brain arteriovenous malformation (AVM).

An AVM is an abnormal tangle of blood vessels in the brain or spine which diverts blood from the arteries to the veins.

Jack spent three hours receiving targeted radiotherapy on Tuesday at Macquarie University Hospital in Sydney as part of the procedure which aims to destroy the residual bit of his AVM, and reduce his risk of haemorrhaging on the brain to zero.

Gamma Knife Surgery Program neurosurgical director John Fuller told AAP the traditional method of surgery to remove an AVM would not work as it was too deep in the brain.

Dr Fuller said Jack's AVM had been partially obliterated with linear accelerator radiosurgery five years ago but more had to be done to give him the best chance of not having haemorraghing in the future.

"We are able to contain the dose fairly specifically (with Gamma) ... and it lowers his risk of haemorrhage," he said.

The procedure involved a fixed frame for the skull that creates the much higher accuracy.

A scan in three months will hopefully reveal how the procedure went but the full results won't be known for years, Dr Fuller said.

Macquarie University Hospital brought the technology to Australia eight years ago.

Jack's mother Christine Ottens told AAP the only reason they found about his condition at age five was he hit his head outside a library in Melbourne and scans revealed the birth condition.

"It was probably a good thing he had a head injury because we would never have found out."

Then in April 2016, at almost age 10, Jack had an AVM.

Mrs Ottens said Jack had headaches and had been vomiting prior to his episode before being eventually treated by the medical team at Monash Medical Centre in Clayton.

But then he had another one six months later, though not as bad as the first.

Mrs Ottens went on the hunt for the best treatment for her son and found it in Australia's backyard - Gamma Knife Surgery - which had an 80 per cent chance for his survival unlike 50 per cent for other treatments.

"It is absolutely miraculous he is still alive. You would never know there is anything wrong."

"Jack has had over 600 absences from school and has had to attend more than 200 medical appointments each year," she said.

Jack's also battling hydrocephalus which occurs when there is excess fluid in the brain which can cause severe disability or death.

Mrs Ottens and her husband Chris remortgaged their house three times to cover the cost of Jack's treatment and put their Berwick home on the market to deal with more than $500,000 worth of debt.

But thankfully this procedure was aided with donated money from a fund at the hospital.

Australian Associated Press