I wrote the example. An American freelancer I hired to check my essay added the bold sentence for me. According to the dictionary, "lines of work" means the work that a person does regularly in order to earn money. But in my example, the doctor wants to go to Africa to save lives, not to earn money. In this case, do you think his use of "lines of work" works?
There are lines of work only accessible in some regions. For example, A doctor trained in Switzerland might want to give up their current quality of life to go practice in Africa to help the most vulnerable.