Y Gonzalez*, B Meng, D Parsons, B Hrycushko, T Zhuang, B Cai, Y Zhang, K Westover, P Iyengar, A Godley, S Jiang, M Lin, University of Texas Southwestern Medical Center, Dallas, TX

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  Y Gonzalez

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TU-D1000-IePD-F2-3 (Tuesday, 7/12/2022) 10:00 AM - 10:30 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 2

Purpose: In this study, we report our pioneering experience to apply the emerging CBCT-based adaptive radiotherapy (ART) for stereotactic ablative radiation therapy (SAbR) treatment of early stage non-small cell lung cancers or metastases to the thorax.

Methods: We considered 18 patients treated using daily ART with total prescribed dose ranging from 33-60Gy over 3-5 fractions. A template was developed following RTOG-0915 as guidance for initial pre-plan. Ring structures were incorporated to control dose fall-off. During ART, thorax fast CBCT was acquired on which physicians contoured targets/OARs. Adaptive plan was re-optimized for patient anatomy of the day based on initial pre-plan. ITV volume was recorded over the course of treatment. We report dosimetric improvements in coverage, conformality, gradient, OAR sparing of the adaptive plan. Timing data from CBCT acquisition through treatment start were recorded to demonstrate ART efficiency.

Results: Based on our analysis of 68 adaptive fractions, adaptive plans were selected by the physician 88.2% of the time. The volume of ITV contoured by physician reduced in 54.4% of fractions with mean reduction of 24.3%. ITV volume from CBCT at 1st ART fraction differed from that on CT by 14%. Frequency of scheduled and adaptive plans meeting RTOG target objectives was 87.9% and 91.5%, while OAR objectives were met at 93.9% and 96.6%, respectively. Comparing adaptive plan to scheduled plan, PTV and ITV coverage improved by 2.99% (p=0.009) and 1.07% (p=0.005), while R50 and R100 improved by 62.5% (p=0.05) and 66.7% (p=0.098), with comparable OAR-sparing. The adaptive process took ~15 minutes on average (contouring 9min, optimization 5min, QA 1.5min).

Conclusion: Over 50% of patients demonstrated an ITV change during 1-2 week ART. We presented a robust workflow from planning to ART and found ART improved target coverage, dose conformity, and comparable OAR sparing, which demonstrates the efficiency and effectiveness of ART.

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