The surgery Mr Chandler performs carries big risks
"It's like a high stakes poker game, but when you win, you win big," says neurosurgeon Chris Chandler.
He is one of the few surgeons in the UK who is able to perform delicate, but potentially life changing operations for young people with epilepsy.
He and his team at King's College Hospital in London use cutting-edge technology to pinpoint the precise area of the brain that is misfiring and remove it surgically.
BBC One's "Your Life in their Hands" shadowed Chris as he treated two patients - Sarah Mole who is 18 and Harry Davidson who is seven.
Sarah had surgery for her epilepsy three years ago, but unfortunately her seizures returned with a renewed ferocity - she can have more than 22 seizures a day.
Sarah finds it extremely disabling.
"I can't go out on my own. I'm just fed up with it and just want everything sorted."
Harry's fits are life threatening - they can stop him breathing - and can't be controlled with seizure medication.
The constant disruption in his brain means he has trouble learning new information at school.
In the playground, Harry has to wear a red cap to make him stand out from his class mates so that the staff can find him in a hurry should he need urgent medical attention.
His parents worry what his future will hold.
Harry's dad Glen said: "You deal with it because you have to. It's life or death stuff. We feel that we are sitting on a time bomb."
Deciding whether to opt for surgery is a difficult one to make because the procedures are risky.
Mr Chandler said: "To think that your delving around within the skull could utterly alter that patients psyche, their personality, their ability to interact, communicate and function in society is really a huge responsibility.
"But in a way you are treating a person who has a disease process. At some point you have to accept that you are there to fix a problem."
Before the operations could go ahead, Mr Chandler and his team needed to check where in the brain the seizures originate.
In Sarah's case, this required a two-hour operation to insert electrodes into the suspect areas that will record any seizures she has over the next seven days.
Sarah's surgery left her with permanent injury to her sight
Mr Chandler said: "The scariest thing when you are operating on the brain is when you get bleeding that you can't control. Sometimes it gets very hairy."
There is also a risk that nearby brain structures that control functions such as speech and vision will be damaged.
Unfortunately, Sarah developed a blood clot after the surgery that had to be removed urgently. This left her with some speech problems.
However, the electrodes showed that her seizures were coming from some tissue that had not been completely removed during her original epilepsy surgery three years ago.
When Sarah was well enough three weeks later, Mr Chandler operated again to remove this tissue.
The surgery was particularly tricky because of the scarring from Sarah's previous operations.
Mr Chandler said: "We went for broke in terms of what we were taking out because it was important to make sure that we got absolutely every last area that might be causing the seizures."
The surgery was a success and Sarah has been free of seizures for four months. However, because of the extent of tissue that had to be removed, she has lost some peripheral vision and can no longer see things clearly to her right.
Mr Chandler said: "It's never nice to have to talk to somebody about the deficit you might inflict, and even more difficult to see that a patient has got a deficit.
"Every neurosurgeon has had to face that."
For Harry, the chance of success was lower - around 50% - because it was not completely clear whether the area that Mr Chandler planned to operate on would turn out to be the cause of his epilepsy.
However, his parents decided along with Mr Chandler's team that it was worth the risk.
During the operation it was obvious that the site in the brain that Mr Chandler had suspected was diseased was indeed the root cause of Harry's epilepsy.
One month on and Harry has had no more fits.
Glen said: "In every aspect he is a changed boy."
Mr Chandler said: "To have a mother and a father say 'you have given us back our child'...what a buzz that is. That more than counteracts the destruction and the grief that sometimes surrounds neurosurgical cases."
Your Life in their Hands will be shown Wednesday 27 July, 9pm, BBC One.