Room: Exhibit Hall | Forum 6
Purpose: Proton beam has attractive properties having the finite range in patient attributed to its Bragg peak. However, these properties make proton dose distribution very sensitive to variations of water equivalent path length (WEPL) through tissues. Proton radiography may be used for validating such variations in treating mobile tumors, for example, tumors in the lung. We performed Monte-Carlo simulations (TOPAS) of proton radiography imaging for a lung cancer patient, using the single detector energy-resolved proton imaging technique.
Methods: A single detector proton radiography system (SDPRS) has been constructed in TOPAS by following a newly proposed proton beam radiography technique based on energy resolved dose functions (ERDF). The system includes a Mevion HYPERSCANâ„¢ pencil beam scanning treatment head and a 2D dose detector. Simulations were first performed for a series of monoenergetic proton beams penetrating different depths of water to construct a calibrated ERDF collection serving as a â€œrulerâ€? for WEPL derivation. CT image dataset of a lung cancer patient at each respiration phase was then converted into a specific voxelized phantom, with its tumor area subsequently imaged by SDPRS to produce a proton radiograph in anterior-posterior direction for the particular respiration phase.
Results: A proton radiograph series of lung tumor over the entire respiration cycle with 1 mm spatial resolution was obtained from our simulations. The tumor was clearly visible on the proton radiographs at all respiration phases. The tumor motion over the respiration cycle was also accurately tracked by the proton radiographs.
Conclusion: There generally exist nonnegligible WEPL variations along the beam path between different respiration phases for lung cancer patient. Real time proton radiographs obtained by pencil beam systems like HYPERSCAN could allow one to easily locate tumor and evaluate the tumor motion and WEPL variations caused by respiration.
Funding Support, Disclosures, and Conflict of Interest: Dr. Townsend Zwart and Dr. James Cooley are the employees of Mevion Medical Systems Inc.