(Wednesday, 8/1/2018) 1:45 PM - 3:45 PM
Room: Davidson Ballroom A
Purpose: Robust optimization (RO) has been adopted to ensure robustness of intensity modulated proton therapy (IMPT) treatment plans in face of physical uncertainties such as range and setup errors, where the relative biological effectiveness of protons is assumed of a simplified constant. In this study, we added objectives based on biological dose into the conventional RO cost function to investigate the impact of RO on biological dose distributions of IMPT.
Methods: One patient with head and neck (H&N) cancer and one with prostate cancer were selected to for this study. Three plans were generated for each patient: PTV-based optimization, conventional RO and biological based RO (BioRO). In BioRO, the sum of differences between the best and worst biological dose, approximated by the product of linear energy transfer (LET) and physical dose, in each voxel were added to a voxel based worst case RO cost function. Both constant RBE (1.1) weighted dose (RWD) and LET weighted dose (LETxD) of nominal scenario were used to evaluate and compare the plan quality. Dose volume histograms (DVHs) bands based on uncertainty scenarios were used to quantify plan robustness.
Results: Comparing PTV-based plans with RO plans, RO plans were more robust than the PTV-based plans in terms of RWD, but no evident advantage of plan robustness was observed for RO plans in terms of biological dose. Comparing BioRO plans with RO plans, BioRO plans not only showed similar plan quality and robustness to the RO plans in terms of RWD distributions, but also achieved significantly improved plan robustness of biological dsoe for both target and critical structures.
Conclusion: Biological based robust optimization was shown to be able to achieve robust biological dose of IMPT with respect to physical uncertainties in our study of two patient cases.
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