An apparatus for use in a treatment planning process or in a treatment process, includes: an input for obtaining a parameter representing a number of beam on-off transitions； and a treatment planner configured to optimize a treatment plan based on parameter representing the number of beam on-off transitions. An apparatus includes: an input configured to obtain a width of a gating window for a treatment plan； and a gating window adjustor configured to adjust the width of the gating window during a treatment session. An apparatus includes: a dose calculator configured to calculate doses for different treatment variations； an evaluator configured to evaluate treatment acceptance criteria against the calculated doses； and a delivery limit module configured to determine one or more limits for one or more delivery parameters based on an evaluation of the treatment acceptance criteria by the evaluator.
