Using Kilovoltage Triggered Imaging to Improve Intrafraction Motion Management for Free Breathing and Breath Hold Lung Stereotactic Body Radiation Therapy
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PO-GePV-T-432 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Stereotactic Body radiation therapy (SBRT) is a commonly used focal treatment for inoperable primary and metastatic lung tumors. During Lung SBRT a high biologically effective dose (BED)>100Gy is delivered over a few (1-5) fractions, which requires an accurate dose delivery to tumors while sparing high dose to surrounding healthy tissues. This makes respiratory motion management techniques very crucial, as outlined in the AAPM TG-76 report.
Methods: Total number of 173 triggered images from 28 treatment fractions of 7 patients were analyzed in this study. For 3 patients (four sites) breath hold technique using Active Breathing Coordinator (ABC) was utilized to reduce the tumor motion. Three repeated breath hold scans were acquired during simulation and ITV were delineated by combining the GTVs from repeated scans. KV triggered images were acquired at the beginning of each breath hold during delivery. The other four patients were treated with free breathing. An abdominal compression belt was used during both simulation and treatment to minimize the range of tumor motion. A 4D-CT was acquired during simulation and ITV was generated based on the range of tumor motion during respiration cycles. Triggered images were acquired in every 60 degrees of gantry rotation during treatment. PTV was generated by 5mm symmetrical expansion of ITV in both techniques. For analysis the GTV on the triggered images were compared with the ITV, and PTV contours from the planning CT.
Results: Using ABC technique, average percentage of tumor (GTV) volume covered by ITV and PTV were 88.9% ± 6.5%, and 99.6% ± 0.9% respectively. With free breathing and compression belt, average tumor volume covered by ITV and PTV were 89.2% ± 7.6%, and 99.6% ± 1.0%.
Conclusion: Kilovoltage triggered imaging provides an effective intrafraction motion monitoring for lung SBRT, and can improves intrafraction motion management substantially.
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