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CT Ventilation Image-Guided Functional Adaptive Radiotherapy for Locally Advanced Lung Cancer

T Yamamoto

T Yamamoto1*, S Kabus2 , M Bal3 , K Bzdusek4 , P Keall5 , C Wright1 , S Benedict1 , M Daly1 , (1) University of California Davis, Sacramento, CA, (2) Philips Research, Hamburg, Germany ,(3) Philips Healthcare, Best, Netherlands,(4) Philips Healthcare, Fitchburg, WI, (5) University of Sydney, Camperdown, Australia


TU-H-605-1 (Tuesday, August 1, 2017) 4:30 PM - 6:00 PM Room: 605

Purpose: Lung functional image-guided radiotherapy (RT) that avoids irradiating highly-functional regions is currently under investigation through several clinical trials. Tumor regression during a course of RT is common in lung cancer, which can lead to recovery of lung function. Adaptive RT that accounts for such changes have not been explored. We hypothesized that functional adaptation with CT ventilation imaging, an emerging modality, significantly reduces the functional lung dose compared to conventional planning schemes.

Methods: Repeat CT scans were acquired before RT and after approximately 20 Gy and 34 Gy for 11 patients with locally advanced lung cancer enrolled on an ongoing clinical trial. Ventilation images were calculated by deformable image registration (DIR) of 4D CT image sets and image analysis. Four IMRT plans were created for each patient: (1) functionally-adapted, (2) anatomically-adapted, (3) functionally-unadapted, and (4) anatomically-unadapted. Functional plans were designed to selectively avoid highly-functional lung regions and meet standard constraints, while anatomical plans were designed to meet standard constraints only. Adaptation was performed after both 20 Gy and 34 Gy. DIR was used for accumulating dose and ventilation. A paired t-test was used to compare the accumulated dose metrics of the four plans.

Results: Tumor volume decreased by 18% after 20 Gy (p=0.05) and 32% after 34 Gy (p=0.02) on average. Lung dose-function metrics (mean dose, V10 and V20) were all significantly lower in the functionally-adapted plans than in the other three plans with similar target coverage. Functional adaptation reduced the lung functional mean dose by 3.9% (p=0.01), 5.2% (p=0.02), and 6.6% (p=0.02) compared to anatomically-adapted, functionally-unadapted, and anatomically-unadapted plans, respectively.

Conclusion: CT ventilation image-guided functional adaptive RT has been demonstrated to significantly reduce the functional lung dose compared to conventional planning schemes, indicating the potential to further reduce the risk of pulmonary toxicity.

Funding Support, Disclosures, and Conflict of Interest: This study was supported in part by the American Cancer Society and the Dean of the UC Davis School of Medicine (ACS IRG-95-125-13). SK, MB and KB are employees of Philips.

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