Characterization of patient-specific, respiration-related features. The breathing pattern is quantified using two volume ratios: the external ((tVC/TVC)Max) and the internal ((ΔVEXP/ΔVLung)Max). The stage-averaged conversion factor is approximately a constant for all patients. From the reference ‘piston’ position (0 mm) to a displacement (ΔZ = 15 mm), the volume variation (α = (V15−V0)/V7.5) smaller than 3% is considered a cylindrical rib cage, while three patients (#6, #9 and #11) have conically shaped rib cages (>3%). For up to 30 mm motion range, an approximate linear volume increase was found (R2 = 0.95). Equation (11) or (12) was used for calculating diaphragm displacement, depending on the volumetric shape.