Guertin is the former CEO of Varian Medical Systems. During his more than 35 years with the company, he was not only the CEO but also held a number of senior management positions, including executive vice president, chief operating officer, and president of Varian's oncology business unit.

He is also a member of Teradyne's board of directors and chair of the Global Access to Cancer Care foundation. Guertin's appointment to Varex's board has pushed the number of directors to eight.

Varex was spun out of Varian in 2016 when the company's Imaging Components business was launched as an independent company.