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Robust Beam Orientation Optimization for Intensity-Modulated Proton Therapy

W Gu1*, R Neph1 , D Ruan1 , J Zou2 , L Dong2 , K Sheng1 , (1) UCLA School of Medicine, Los Angeles, CA, (2) University of Pennsylvania, Philadelphia, PA


(Monday, 7/15/2019) 1:45 PM - 3:45 PM

Room: Stars at Night Ballroom 2-3

Purpose: To integrate robust beam orientation optimization (BOO) and robust fluence map optimization (FMO) in a unified framework for Intensity Modulated Proton Therapy (IMPT).

Methods: The framework is formulated with a dose fidelity term, a heterogeneity-weighted group-sparsity term, and a sensitivity regularization term. The L2,1/2-norm group-sparsity reduces the number of active beams from 1162 non-coplanar candidate beams, to 2-4. A heterogeneity index, which evaluates the beam-specific lateral tissue heterogeneity, is used to weigh the group sparsity term, to encourage beams more resilient to setup uncertainties. By integrating sensitivity regularization, the framework further improves beam robustness against both range and setup uncertainties. This Sensitivity regularization and Heterogeneity weighting based BOO-FMO framework (SHBOO-FMO) was tested on two skull-base tumor patients and two bilateral head-and-neck patients. The conventional CTV-based optimized plans (Conv) with SHBOO-FMO beams (SHBOO-Conv) and manual beams (MAN-Conv) were compared for beam robustness. The dosimetry and robustness of SHBOO-FMO plan were compared against the manual beam plan with CTV-based voxel-wise worst-case scenario approach (MAN-WC).

Results: With SHBOO-FMO method, the beams with superior range robustness over manual beams were selected while the setup robustness was maintained or improved. With range uncertainties, SHBOO-Conv increased the average lowest [D95%, V95%, V100%] of CTV from [93.85%, 91.06%, 70.64%] in MAN-Conv, to [98.62%, 98.61%, 96.17%]. With setup uncertainties, the average lowest [D98%, D95%, V95%, V100%] were increased from [92.06%, 94.83%, 94.31%, 78.93%] in MAN-Conv, to [93.54%, 96.61%, 97.01%, 91.98%] in SHBOO-Conv. Compared with the MAN-WC plans, the final SHBOO-FMO plans achieved comparable robustness and better OAR sparing, with an average reduction of [Dmean, Dmax] of [4.88, 5.82] GyRBE from the MAN-WC plans.

Conclusion: We developed a novel method to integrate robust BOO and robust FMO into IMPT optimization for a unified solution of both BOO and FMO, generating plans with superior dosimetry and good robustness.

Funding Support, Disclosures, and Conflict of Interest: This research is supported by NIH Grants Nos. R44CA183390, R43CA183390 and R01CA188300.


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