One provides a first dose-volume histogram (DVH) constraint as pertains to controlling localized excessive-radiation dosage with respect to a particular treatment volume. One then automatically determines whether to supplement this constraint by using an adaptive DVH constraint. These teachings will accommodate determining whether to supplement the first DVH constraint, at least in part, by determining whether a user has specified such supplementation (using, for example, a corresponding user interface) by, for example, placing at least one DVH constraint such that the constraint corresponds to a volume fraction at a range boundary.