Information is provided regarding a blocks sectional contour in a particular plane as corresponds to a radiation-therapy beam. For a point at which block effects are to be assessed, a point is projected onto a plane of the block and a plurality of straight lines is then formed. Each line has a particular relationship with respect to the projected point (such as having each such line intersect all others at the projected point). Intersections amongst these straight lines and the contour are used to evaluate corrections to the dose at the point. These teachings will accommodate identifying line segments that are located within the contour and that are bound by the intersections with the contour. Elementary contributions as correspond to each of these line segments can be averaged to evaluate delivered dose corrections that are due to the presence of beam-limiting and beam-shaping devices in the particular treatment plan.
