Optimum Gating Window for Gated Carbon-ion Beam Liver Treatment Planning using 4DCT Data

One of the important factors in liver radiotherapy is considering the intrafractional movement, especially in carbon-ion beam treatment, because respiratory induced liver motion is relative larger than other thoracic and abdominal sites. As a result, particle range variation could be expected significant large due to density variation by replacing lung and liver densities. We, therefore, evaluated the intrafractional carbon ion dose variation using a 4DCT data set. Patients with liver cancer were subject to the 4DCT examination under free-breathing conditions. Planning target volume (PTV) were defined by adding internal margin of 1.0 ~ 1.2 cm to GTV. Compensating bolus was designed for the PTV at peak-exhalation phase. Carbon ion dose distributions were calculated by applying the compensating bolus to the 4DCT data set. We assessed 4D dose volume histograms (4D-DVH) by using deformable registration.6th Japan-Korea Joint Meeting on Medical Physics (JKMP) and 11th Asia-Oceania Congress of Medical Physics (AOCMP