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Session: Multi-Disciplinary: Imaging for Motion Management [Return to Session]

Tumor Motion Tracking in a KV Scattered X-Ray Imaging System for Lung Cancer Radiotherapy

Y Zhong1*, T Chiu1, Y Huang1, Y Shao1, C Shen1, K Yang2, X Jia1, (1) UT Southwestern Medical Center, Dallas, TX, (2) Harvard Medical School, Massachusetts General Hospital, Boston, MA


TH-IePD-TRACK 3-6 (Thursday, 7/29/2021) 12:30 PM - 1:00 PM [Eastern Time (GMT-4)]

Purpose: Tumor motion tracking is a critical component of lung radiotherapy. We previously proposed a new scheme of using kV scattered x-ray photons for marker-less tumor tracking and presented the imaging capability of using photon-counting detection. This study investigates suitability of this technique for tumor motion tracking accuracy via experiments and Monte Carlo (MC) simulations.

Methods: A CIRS lung phantom was used in the measurements and modeled in the simulation. The targeted tumor with a diameter of 2 cm was aligned to the iso-center. The collimated primary X-rays from the on-board kV X-ray tube illuminated the tumor from 45° gantry direction. The scattered X-rays were detected using a photon-counting detector (XC_THOR, DirectConversion, Sweden) with a parallel multi-hole collimator. The kV x-ray technique was 120 kVp and 10 mAs (200 mA, 50 ms). Exposure time of 50ms was selected to achieve a 10 Hz imaging speed. An MV beam (6 MV, 600 MU/min, 2x2 cm^2) was used to study the performance during treatment delivery. To investigate the tumor-tracking accuracy, we moved the couch in 1 mm steps in the superior-inferior (SI) direction in experiments. In MC simulation, the tumor was moved with a speed of 1 cm/s in the SI direction and along the kV beam direction. We tracked the tumor position in the scattering images using template-matching and compared with the ground truth.

Results: The tumor can be visually identified clearly on the measured and the simulated kV scattered X-ray images. The measured tumor positions agreed well with the ground truth positions in the experiments and the simulation study, with the mean error of 0.65 mm and 1.0 mm for the experiments and simulation respectively.

Conclusion: The experiments and simulations demonstrated sufficient motion tracking accuracy of real-time tumor tracking using the proposed technique.



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