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Biological Effectiveness-Integrated Beam Orientation Optimization for Intensity-Modulated Proton Therapy

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


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

In IMPT, ignoring variation in biological effectiveness contributes to the discrepancy between the constant RBE prediction and experimental observations. Incorporating RBE in treatment planning would reduce the discrepancy and improve the therapeutic ratio. A method incorporating biological effectiveness into beam orientation optimization (BOO) is still unavailable. In this study, we developed a novel BOO framework integrating physical and biological doses.

This biological effectiveness integrated BOO (BioBOO) framework includes physical dose fidelity, LET×D constraints, and group sparsity conditions. The LET×D of OARs are penalized to minimize the biological effective dose while maintaining physical dose objectives. Group sparsity is used to select 2-4 active beams from 600-800 non-coplanar candidates. Our approach was tested on three skull-base-tumor (SBT) patients and three bilateral head-and-neck (H&N) patients. The BioBOO plans were compared with IMPT plans using manually selected beams with only physical dose constraints (MAN) and the MAN plan reoptimized with additional LET×D constraints (BioMAN).

BioBOO plans show superior physical and biological dose sparing. On average, the [mean, maximal] doses of OARs in BioBOO are reduced by [2.85, 4.6] GyRBE from MAN in the SBT cases and reduced by [0.9, 2.5] GyRBE in the H&N cases, while BioMAN is comparable to MAN. cLET×D (c is a scaling factor of 0.04 µm/keV) of PTVs are comparable in BioBOO and BioMAN. On average, in the SBT cases, BioBOO reduces the OAR [mean, maximal] cLET×D by [1.1, 2.9] Gy from MAN, compared to the reduction by BioMAN from MAN of [0.7, 1.7] Gy. In the H&N cases, BioBOO reduces the OAR [mean, maximal] cLET×D by [0.8, 2.6] Gy from MAN, compared to the reduction by BioMAN from MAN of [0.3, 1.2] Gy.

We developed a novel biological effectiveness-integrated BOO method for IMPT to generated plans with improved physical and biological OAR sparing.

Funding Support, Disclosures, and Conflict of Interest: NIH Grants Nos. R44CA183390, R43CA183390, and R01CA230278


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