Four-dimensional dose reconstruction system for lung cancer VMAT treatment: a 4D phantom study

Background: recently, volumetric modulated arc therapy (vmat) has been applied to the treatment of moving targets, such as lung tumors. the displacement of actual tumors during treatment based on an averaged four-dimensional (4d) planning computed tomography (ct) image set induces inconsistencies between dose distribution determined during the treatment planning step and the actual irradiated dose. the present study introduces a 4d dose reconstruction system and demonstrates its feasibility based on the results of dynamic thorax phantom experiments. materials and methods: linear accelerator log files of two types— dynamic beam delivery log files and dynalog files—were used to create the dicom-rt plan file with multiple-field irradiation. dose distribution corresponding to each respiratory phase was calculated by planning the corresponding ct image set, and the accumulated dose distribution was subsequently reconstructed. in the experiment conducted in this study, two types of lung-tumor motion were considered—linear motion in the craniocaudal direction and combined motion in the craniocaudal and rotational directions. results: the dose delivered to the center of a tumor was observed to vary by up to 4.4 %, depending on the initiation time of vmat irradiation—the proposed system estimated the administered dose with an accuracy of 1.3 % or less. in the case of two-dimensional dose distribution, the pass rate of gamma analysis with a tolerance of 3 mm/3 % exceeded 96.6 %. conclusion: the proposed system exhibited high dose-estimation accuracy for intricately moving targets, e.g., lung tumors, undergoing combined linear and rotational motion.