Evaluation of the material assignment method used by a Monte Carlo treatment planning system

An evaluation of the conversion process from Hounsfield units (HU) to material composition in computerised tomography (CT) images, employed by the Monte Carlo based treatment planning system ISOgray™ (DOSIsoft), is presented. A boundary in the HU for the material conversion between “air” and “lung” materials was determined based on a study using 22 patients. The dosimetric consequence of the new boundary was quantitatively evaluated for a lung patient plan.