Impact of inline magnetic fields on dose distributions for VMAT in lung tumor.

Abstract

The purpose of this study is to investigate the impact of inline magnetic field on dose distribution for volumetric modulated arc therapy (VMAT) in lung tumors located at the chest wall and mediastinum. Two VMAT plans for a thorax phantom with lung tumors of 1\u202fcm and 2\u202fcm in diameter located at the chest wall were created by a treatment planning system. Next, five clinical VMAT plans for a non-small cell lung cancer (NSCLC) at early stages I and II of 5\u202fcm or less in diameter were also used. The planning target volume (PTV) sizes were in the range from 11.1 to 82.7\u202fcm3. The prescription dose was 60\u202fGy for D95 in the PTV. The VMAT dose distributions without and with uniform inline magnetic field of 0.5\u202fT and 1.0\u202fT were calculated using the Monte Carlo method. The dose distributions were analyzed by dose volume histograms, dose differences, and dose indices. In all VMAT plans, the PTV dose was enhanced by inline magnetic field. The dose enhancement was larger with 1.0\u202fT than with 0.5\u202fT. In phantom plans, D98 in the PTV with 0.5\u202fT and 1.0\u202fT increased by 2.9-6.6\u202fGy and 3.9-9.8\u202fGy, respectively, in comparison with that at 0\u202fT. Similarly, in clinical plans, it increased by 2.2-6.0\u202fGy and 3.9-10.7\u202fGy, respectively. Thus, the VMAT with the inline magnetic field was proved useful for the dose enhancement in the lung tumor located at the chest wall and mediastinum.