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Image Acquisition Optimization of a Limited-Angle Intrafraction Verification (LIVE) System for Lung Radiotherapy

Y Zhang

Y Zhang1*, X Deng2 , F Yin1 , L Ren1 , (1) Duke University Medical Center, Durham, NC, (2) Duke Kunshan University, Kunshan, Jiangsu, China


SU-E-601-3 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 601

Purpose: LIVE has been previously developed for 4D intrafraction target verification during arc delivery or between 3D/IMRT beams [1]. Preliminary studies showed that LIVE can reconstruct the target volume for each respiratory phase accurately using kV/MV projections acquired at 1 degree/projection over orthogonal-view 30° scan angles. However, such acquisition requires very slow gantry rotation, which may not always be clinically preferable. The goal of this study is to optimize the image acquisition of LIVE for different breathing scenarios and clinical gantry rotation speeds, which is imperative for the clinical implementation of LIVE.

Methods: LIVE was investigated for breathing cycles varying from 3 to 6 seconds and gantry rotation speeds varying from 0.3°/s to 6°/s. The minimum number of respiratory cycles that need to be scanned and minimum kV and MV projection numbers needed to reconstruct 4D target volume were determined for each scenario using the anthropomorphic XCAT phantom. Various respirational changes from planning 4D-CT to onboard volume and tumor size/locations were simulated in XCAT to study the robustness of LIVE. The CIRS phantom was used to further evaluate the optimized imaging scheme from XCAT study.

Results: Gantry rotation speeds of 2-6°/s, 1°/s, 0.6°/s, and 0.3°/s required scanning of 4, 6, 12 and 18 respiratory cycles respectively for breathing cycles of 3-4s, and 4, 6, 9 and 12 respiratory cycles respectively for breathing cycles of 5-6s. Minimum kV and MV projections needed per cycle were 2, 2, 1 and 1, respectively. The optimized LIVE was robust against anatomical and breathing changes. In CIRS study, the optimized LIVE system achieved the average center-of-mass-shift (COMS)/volume-percentage-difference (VPD) of 0.2±0.1mm/6.1±1.2% among all gantry rotation speeds tested.

Conclusion: The optimized image acquisition greatly improves the efficiency of LIVE while minimizing the imaging dose, which substantially enhances its applicability for 4D intrafraction verification of lung SBRT.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by NIH grant R01 CA-184173.

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