trim down an arc and use a suitable Contour toolpath

draw a pair of nested circles and a polygon/polyline which defines the arc which one wishes to cut and and use Boolean operations to arrive at the desired area definition

draw a pair of nested circles and a polygon/polyline which defines the arc which one wishes to cut and and use the Trim Vectors and Join Vectors commands to arrive at the desired are definition

Doing this using Boolean operations is similar, but one needs two circles, one to describe the shape which will be left, the other which is offset by tool diameter plus ~10%: