The term Sensei is greatly misunderstood in martial arts circles. It is not a title like “Mr. or Coach” as one would use those words in the West. but more an indications of the standing of the person to whom it is applied. So, for example, just because somebody is teaching a class does not mean that he is a “Sensei” or even that he should be called such. However, if he has been training for many years, has received high grades from acknowledged experts, and is widely respected by his peers, he would normally be referred to by this title, but only after his family name. For example, Kinjo Sensei. To a native Japanese speaker it would sound very odd if someone was referred to as “Sensei Smith” as the descriptive word always comes after the family name.
In Japan physicians and lawyers are automatically referred to as Sensei.