The doctor makes a great hero in a romance novel. Why? He has power, compassion, brains, and money. He's able to take on any problem and solve it, through all his qualities. He can also heal people, even the most vulnerable.
Heroines can also be a doctor, but if your reader is a woman, my guess is the male being a doctor is more touching to the reader (in most cases). Here's why--women are normally more compassionate (now don't beat me up, because there are exceptions to this rule) and are usually more in touch with their emotions. So for a man to show these qualities are usually (and not always) more difficult than for a woman to show compassion.
Writing about a doctor is kind of fun, because of the research involved in whatever they're working on. Also, if the man is the doctor, then the writer is missing the mark if they don't include some sort of medical emergency.
What does a doctor go through? I have a friend who's married to a doctor. The stress on their life is intense. Every decision can be a life-and-death emergency. They're also on call many days of the week, even when they're having other life issues. They have to keep their medical licenses updated (and take tests for every specialty), and take courses to stay current.
Sometimes, their patients can be a pain (trust me...I have a feeling I'm one of those types). If they do anything wrong, they can and will be sued. Any bad treatment (sometimes, they're split second decisions) can end a life.
Their schooling lasts at least eight years, many times more, dealing with specialties. They might make decent money when out in a practice, but their college bills and malpractice insurance can take their tolls on salaries.
So when writing about the doctor, realize they're not just healers. They're compassionate people who are dealing with stress that most of us can't even imagine.
Have a great day!
Sweet Tale Books