Diaphragm motion range during controlled breath-holding at three different inspiratory levels was assessed during dynamic MRI employing an Active Breathing Coordinator (ABC). Colour intensity projections displayed diaphragm position with time. Diaphragm displacements were calculated from difference images between the end and beginning of breath-holds. Overall, diaphragm volume displacements were smaller for the 75% deep inhalational volume (DIV) threshold typically applied in lung and breast radiotherapy, than for the shallower inspiratory levels of 50% and 25% DIV. The clinical standard 75% DIV threshold not only expands the lungs more but also decreases diaphragm motion range.
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