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

PURPOSE

This 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 METHODS

Pairs (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.

RESULTS

The average internal motion in end-expiration was 1.1mm, which was significantly smaller than that in end-inspiration. The mean deviation from the plan was -0.1, 0.3, and 0.1mm in the left-right (LR), cranio-cepharal (CC), and anterior-posterior (AP) directions, respectively. The estimated PTV margins were 3.2, 3.5, and 4.6mm, in the LR, CC, and AP directions, respectively.

CONCLUSIONS

It 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.