Abstract
Purpose: To develop and test an integrated simulation system based on the digital Extended Cardio Torso (XCAT) phantom for 4-dimensional (4D) radiation therapy of lung cancer. Methods: A computer program was developed to facilitate the characterization and implementation of the XCAT phantom for 4D radiation therapy applications. To verify that patient-specific motion trajectories are reproducible with the XCAT phantom, motion trajectories of the diaphragm and chest were extracted from previously acquired MRI scans of five subjects and were imported into the XCAT phantom. The input versus the measured trajectories was compared. Simulation methods of 4D-CT and 4D-cone-beam CT (CBCT) based on the XCAT phantom were developed and tested for regular and irregular respiratory patterns. Simulation of 4D dose delivery was illustrated in a simulated lung stereotactic-body radiation therapy (SBRT) case based on the XCAT phantom. Dosimetric comparison was performed between the planned dose and simulated delivered dose. Result: The overall mean (±standard deviation) difference in motion amplitude between the input and measured trajectories was 1.19 (±0.79) mm for the XCAT phantoms with voxel size of 2 mm. 4D-CT and 4D-CBCT images simulated based on the XCAT phantom were validated using regular respiratory patterns and tested for irregular respiratory patterns. Comparison between simulated 4D dose delivery and planned dose for the lung SBRT case showed comparable results in all dosimetric matrices: the relative differences were 0.3%, 4.0%, 0%, and 2.8%, respectively, for max cord dose, max esophagus dose, mean heart dose, and V20Gy of the lungs. 97.5% of planning target volume (PTV) received prescription dose in the simulated 4D delivery, as compared to 95% of PTV received prescription dose in the plan. Conclusion: We developed an integrated simulation system based on the XCAT digital phantom and illustrated its utility in 4D radiation therapy of lung cancer. This simulation system is potentially a useful tool for quality control and development of imaging and treatment techniques for 4D radiation therapy of lung cancer.
Highlights
Respiratory motion hampers the precise delivery of radiation dose to moving targets in radiotherapy of lung cancer [1]
Our goal is to develop a systematic simulation system for characterizing, evaluating, and optimizing advanced radiation therapy of lung cancer based on the XCAT phantom
We have developed simulation methods based on the XCAT phantom for 3D- and 4D-cone-beam CT (CBCT)
Summary
Respiratory motion hampers the precise delivery of radiation dose to moving targets in radiotherapy of lung cancer [1]. Motion phantoms of different forms have been developed and used to study 4D imaging and 4D radiation dose delivery. These phantoms can be broadly divided into three categories: physical phantom [8] [9], physiological phantom [10]-[12], and digital phantom [13]-[16]. There are a few commercial physical phantoms, such as the Dynamic Thorax Phantom by CIRS (CIRS Inc., Norfork, VA, USA) and the Respiratory Gating platform by Standard Imaging (Standard Imaging Inc., Middleton, WI, USA) The drawback of these types of phantom is that the fabrication can be prohibitively expensive for realistic and widely varying geometrical models among patients. The physical and physiological phantoms do not account for patient anatomy and respiratory biomechanics and are sub-optimal for providing guidance for real patient applications
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