Robust Optimization for Intensity-Modulated Proton Therapy to Redistribute High Linear Energy Transfer (LET) from Nearby Critical Organs to Tumors in Head and Neck Cancer.

Robust Optimization for Intensity-Modulated Proton Therapy to Redistribute High Linear Energy Transfer (LET) from Nearby Critical Organs to Tumors in Head and Neck Cancer.:

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Robust Optimization for Intensity-Modulated Proton Therapy to Redistribute High Linear Energy Transfer (LET) from Nearby Critical Organs to Tumors in Head and Neck Cancer.

Int J Radiat Oncol Biol Phys. 2020 Jan 24;:

Authors: Liu C, Patel SH, Shan J, Schild SE, Vargas C, Wong WW, Ding X, Bues M, Liu W

Abstract

PURPOSE: We propose linear-energy-transfer (LET)-guided robust optimization in intensity-modulated proton therapy (IMPT) for head-and-neck (H&N) cancer. This method simultaneously considers LET and physical dose distributions of tumors and organs-at-risk (OARs) with uncertainties.

METHOD: Fourteen H&N cancer patients were included in this retrospective study. Cord, brainstem, brain, and oral cavity were considered. Two algorithms: voxel-wise worst-case robust optimization (RO) and LET-guided robust optimization (LETRO) were used to generate IMPT plans for each patient. The latter method directly optimized LET distributions rather than indirectly as in previous methods. LET-volume histograms (LETVHs) were generated and high LET was redistributed from nearby OARs to tumors in a user-defined way via LET-volume constraints (LETVCs). Dose-volume histogram (DVH) indices, such as clinical target volume (CTV) D98% and D2%-D98%, cord Dmax, brainstem Dmax, brain Dmax, and oral cavity Dmean, were calculated. Plan robustness was quantified using the worst-case analysis method. LETVH indices analogous to DVH indices were used to characterize LET distributions. The Wilcoxon signed rank test was performed to measure statistical significance.

RESULT: In the nominal scenario, LETRO provided higher LET distributions in CTV (unit: keV/μm) [CTV LET98%: 1.18 vs. 1.08, LETRO vs. RO, p=0.0031], while preserving comparable physical dose and plan robustness. LETRO achieved significantly reduced LET distributions in cord, brainstem, and oral cavity, compared with RO [cord LETmax: 7.20 vs. 8.20, p=0.0010; brainstem LETmax: 10.95 vs. 12.05, p=0.0007; oral cavity LETmean: 2.11 vs. 3.12, p=0.0052], and had comparable physical dose and plan robustness in all OARs. In the worst-case scenario, LETRO achieved significantly higher LETmean in CTV, reduced LETmax in brain, and comparable other LETVH indices [CTV LETmean: 3.26 vs. 3.35, p=0.0012; brain LETmax: 24.80 vs. 22.00, p=0.0016].

CONCLUSIONS: LETRO robustly optimized LET and physical dose distributions simultaneously. It redistributed high LET from OARs to targets with slightly modified physical dose and plan robustness.

PMID: 31987967 [PubMed - as supplied by publisher]