At its core, Doctor Zhivago is all about one man's struggle to live the life he wants in a society that constantly orders him to live the life it tells him to. So what better way to acknowledge this individual than to name the book after him?
There are a few different ways to interpret the title.
One interesting fact is that the book isn't called Yuri Zhivago; it's called Doctor Zhivago. By identifying Zhivago by his social role, the book also suggests that Zhivago—whether he likes it or not—has a social responsibility, even though the title does its best to honor him as an individual, too. In other words, Pasternak wants to celebrate the individual—but not too much.
It also suggests that in his own society, Zhivago is better known as a doctor than as a poet. Since he writes poetry that is, ahem, as good as Pasternak's, this is kind of strange. Being a doctor is great, but Zhivago is really a poet. Even in the title of the book, Zhivago is prevented from being fully himself.
One final interpretation is that Zhivago is a doctor in two different ways. He's a doctor by profession, which means that he saves some people's lives and makes other people's lives better. But for both Pasternak and Zhivago, art creates and preserves life, so Zhivago the poet is also a kind of doctor. See our "Character Analysis" for Zhivago for more on this idea.