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Dr. Todd Mainprize, then-head of neurosurgery at Sunnybrook Health Sciences Centre, undated photo. He and his team successfully opened the blood-brain barrier of a living patient.Courtesy of the Family

On Nov. 5, 2015, Toronto neurosurgeon Todd Mainprize and his team accomplished what no one in the world had ever done: Using focused ultrasound waves, they successfully opened the blood-brain barrier of a living patient.

If Dr. Mainprize felt proud of his role in the breakthrough, he didn’t show it.

He was well aware of the significance of this achievement; it was potentially the key to tackling a wide range of illnesses, from brain cancer to Parkinson’s disease and Alzheimer’s disease – illnesses that are currently impossible or hard to cure. But he also knew he and his team at Sunnybrook Health Sciences Centre still had a long way to go before their work translated into actual treatment for patients, said his close friend and colleague Nir Lipsman.

“He greeted [the accomplishment] with an incredible amount of humility and modesty,” said Dr. Lipsman, a neurosurgeon and scientist at Sunnybrook. “He always prefaced everything by saying, ‘Look, we have to study this carefully.’ But he always maintained an optimism that this could be a game-changer in the field.”

Dr. Mainprize died suddenly on June 9. He was 49. As the division head of neurosurgery at Sunnybrook, he was widely respected for his leadership, his contributions to research, his gift for teaching, and his compassion and skill as a brain tumour surgeon. With an encyclopedic knowledge of the brain and a generosity of spirit, Dr. Mainprize was known as the “surgeon’s surgeon,” the person other doctors and surgeons in Toronto would turn to if they needed help with a neurosurgical issue or brain tumour case, Dr. Lipsman said.

“He was in many ways the city’s go-to person for brain tumours,” he said.

He leaves his wife, Susan; their children, Graham, Thomas and Victoria; his mother, Millie (née Snatinsky); his brothers, Eric and Brent; and their families.

He was born on July 3, 1970, in the small town of Outlook, Sask. His father, Gary, was a pharmacist and his mother was a nurse. He was the couple’s middle child.

By around age 10, he already knew he wanted to be a doctor like his grandfather and great-grandfather, his mother said.

As with his interest in medicine, his tendency to avoid the limelight and his drive for mastery were qualities he possessed even as a child. He would later tell his wife that he routinely arose at 5 a.m. while he was growing up to practise his puck-handling skills at Outlook’s only hockey arena or to perfect his serve at the town’s only tennis court.

While everyone else was asleep, he would practise on his own, repeatedly serving the ball from one side of the net and going to pick it up to serve it again from the other.

“He would do that for hours, just to improve on his skills,” she said, noting his pursuit of perfection extended to all his interests and hobbies.

He also had a curiosity for the world beyond his hometown, and talked his parents into hosting foreign exchange students, his younger brother, Brent, said. After graduating high school and with the support of his parents, he chose to spend a year in France, rather than start university right away.

But no matter how far he ventured, he did not forget his humble roots, Brent said. He remained closely connected with his friends and family in Outlook, and later returned with his wife and children to visit every year.

“He didn’t hide where he came from, in fact, quite the opposite,” Brent said, describing his brother as exceedingly unpretentious. “He didn’t really have time for the kind of façade that others may think is important.”

After earning his undergraduate and medical degrees at the University of Saskatchewan, Dr. Mainprize did his neurosurgery residency and research fellowship at the University of Toronto.

In 2000, he met Susan Nguyen, a recent graduate of pharmacy at the University of Toronto, in the cookbook section of a bookstore and the two bonded over their love of cooking. She said she was impressed by his attention to detail and his down-to-earth nature. He arrived on their first date to go ice skating with a warm chocolate croissant and hot cocoa for her. Seemingly hard-wired to put other people’s needs and interests first, he knew little gestures mattered. The couple married in 2004.

As he was nearing the end of his PhD training, he was recruited by Sunnybrook in 2008. Gordon Rubenfeld, chief of the trauma, emergency and critical care program at Sunnybrook, who was part of the recruitment team, said the competition to fill the neurosurgery job was particularly fierce. The hospital was looking for an academic physician, someone who was good at teaching, research and clinical practice, Dr. Rubenfeld said.

“Generally speaking, we’re pretty excited if you can do two of those things really well,” he said, but Dr. Mainprize stood out as a “triple threat.” He turned out, in fact, to be a quadruple threat, if you counted his strength as a leader, Dr. Rubenfeld added.

He didn’t talk much about the need for collaboration and team building. Instead, he led by example, creating an environment where people shared responsibilities and supported one another.

Dr. Rubenfeld, who became a close friend, recalled Dr. Mainprize would join him on his teaching rounds, sharing his knowledge with residents, fellows and nurses who eagerly gathered around to learn from him.

Ms. Mainprize said he often left the house at 4 a.m. to take his residents out for breakfast, knowing that they would have had nothing to eat while on call throughout the night. He also frequently called Ms. Mainprize from the hospital, asking her to order multiple boxes of pizza for the surgical staff who were too busy to have dinner.

A devoted husband and father, Dr. Mainprize rarely missed an opportunity to share photos and stories of his family with his friends at work. Yet at home, even though he enjoyed a rich life separate from the hospital, his patients were never far from his mind.

Dr. Rubenfeld recalled once phoning him while he was away on vacation, just to notify him that one of his patients had been admitted into the intensive care unit during the night and was doing fine. He was surprised to discover Dr. Mainprize was already up to speed, and had reviewed the patient’s lab results and brain scans from earlier that morning.

“On vacation, he was basically as on top of, or more on top of [what was going on with] a patient,” he said.

He spent a great deal of time with his patients, consoling them, providing clear and thorough explanations of their conditions and treatments and making them feel cared for, Dr. Lipsman added.

In addition to his work at the hospital, Dr. Mainprize also joined voluntary humanitarian medical missions to Ukraine in 2015 and 2019 to perform reconstructive surgeries on patients who had been injured in conflict. But as with his contributions to the groundbreaking blood-brain barrier research, he rarely discussed what he had done and did not seek recognition.

For instance, even though they were close friends and colleagues, Dr. Rubenfeld said he didn’t learn the Sunnybrook team had succeeded in opening the blood-brain barrier of a patient until he turned on the radio, and heard Dr. Mainprize being interviewed about it on the BBC. This feat garnered international interest because doctors and scientists have long struggled to safely deliver drugs directly to the brain due to this impermeable barrier around the blood vessels of the brain. Dr. Mainprize likened the blood-brain barrier to cling film, preventing harmful substances in the blood from passing through into the brain.

Using focused ultrasound to cause the expansion and contraction of microscopic air bubbles intravenously introduced into the bloodstream, he and his team showed they were able to create tiny, temporary tears in the barrier that would be large enough for drug molecules to pass through into targeted areas of the brain.

Ever downplaying his achievements and many awards, including the 2007 Sopman Humanitarian Award for exceptional compassion and kindness and the 2015-16 Ross Fleming Surgical Teaching Award, Dr. Mainprize nevertheless cherished the notes he received from his patients. He kept them on display throughout his office.

After his death, Ms. Mainprize collected them all into a large orange shoebox. There were hundreds upon hundreds of cards and letters, all with messages like: “Thanks for doing what you do! You’re a lifesaver.” “You are a miracle doctor!” “I would love to say thank you for your kindness and help.” “Thank you for taking such good care of me.”

He saved every single one.

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