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Robust Optimization Using Four-Dimensional Computed Tomography for the Treatment of Lung Tumors in Pencil-Beam Proton Radiotherapy Planning

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D Cummings

D Cummings*, W Ichter , P Wang , S Tang , C Chang , Texas Center for Proton Therapy, Irving, TX


SU-K-108-14 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 108

Purpose: To evaluate the effectiveness of robust optimization using four-dimensional computed tomography (4DCT) for the treatment of lung tumors in Pencil-Beam Scanning (PBS) proton treatment.

Methods: Proton beam therapy treatments for lung cancer were planned using robust optimization over 4DCT datasets. For robust optimization settings a CT Hounsfield unit (HU) uncertainty of 4% and a setup uncertainty of 5 mm are used. The physician contours the GTV on individual breathing phases (iGTV), and a 5 mm expansion is used to generate the CTV for each phase (iCTV). The target minimum and maximum dose objectives are placed on the iCTV for each individual phase with the aforementioned robustness settings, and the optimization is conducted directly on the 4DCT dataset. Additional target dose objectives as well as OAR requirements are placed on the averaged CT as needed clinically. For comparison, a traditional method of optimization, i.e. optimization on the averaged CT with an ITV was also performed.

Results: The plans were evaluated by the coverage of iGTV and iCTV on all breathing phases of the 4DCT. To compare with the traditional planning method, coverages on the internal gross tumor volume (IGTV) and internal target volume (ITV) are also evaluated on the averaged CT. All plans are normalized such that ITV D99% equals the prescription dose of 70 Gy(RBE). When evaluating on the individual phases, the iGTV coverage D100% and the iCTV coverage D99% are consistently higher for the 4DCT optimized plans in all phases for all patients. However, the lungs V5Gy and V20Gy are slightly larger when using 4DCT for robust optimization.

Conclusion: The treatment plans optimized using 4DCT are more robust when compared to treatment plans optimized on averaged CT only. For proton PBS lung cases, robust optimization on 4DCT is therefore recommended to ensure tumor coverage with minimal OAR effect.

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