Displacement of hepatic tumor at time to exposure in end-expiratory-triggered-pulse proton therapy

PurposeThis study is to evaluate reproducibility of hepatic tumors in end-expiration and end-inspiration on free-breathing, also measure shift of hepatic tumor location in pulsed proton beams exposure in end-expiration in order to estimate feasible planning target volume (PTV) margin.Materials and methodsPairs (1232) of anterior and lateral radiographs from 30 patients (628 end-expiration and 604 end-inspiration phases) were analyzed using fiducial markers adjacent to the tumors. By using the co-ordinates of the marker centroid of mass related to the isocenter, intrafractional variation was compared in end-expiration and end-inspiration, and a feasible PTV margin was generated using the measured motion.ResultsThe average internal motion in end-expiration was 1.1 mm, which was significantly smaller than that in end-inspiration. The mean deviation from the plan was −0.1, 0.3, and 0.1 mm in the left–right (LR), cranio–cepharal (CC), and anterior–posterior (AP) directions, respectively. The estimated PTV margins were 3.2, 3.5, and 4.6 mm, in the LR, CC, and AP directions, respectively.ConclusionsIt was indicated that localization of the targets was more reproducibility in end-expiration than that in end-inspiration. Also, feasible and practical margin values were obtained. These should contribute accuracy of respiration synchronized proton radiotherapy for liver tumors.