Generalized equivalent uniform dose-based biological optimization in hippocampus-sparing whole-brain radiation therapy

Abstract

We applied and evaluated a generalized equivalent uniform dose (gEUD)-based optimization method to hippocampus-sparing whole-brain radiation therapy (HS-WBRT) using volumetric modulated arc therapy (VMAT). Thirteen patients treated with WBRT were enrolled. To investigate the optimal value of the parameter "a" of the hippocampus for optimizing gEUD, we changed value from 1 to 40. Using the determined parameter "a" value for the hippocampus, dose-volume (DV)-based optimization and DV-based gEUD optimization (DV-gEUD) were used to generate HS-WBRT plans for 13 patients. According to the gEUD optimization, the plans for organ at risk (OAR) and the target plus OAR were denoted as DV-(Upper) gEUD optimization and DV-(Upper+Target) gEUD optimization. We analyzed and compared the dose-volume histogram (DVH) of each generated plan. The mean dosage (D-mean) of the hippocampus was lowest when the parameter "a" of the hippocampus was 20, with acceptable compromise of the D-100% and the D-max of the hippocampus. The hippocampus D-100%, D-mean, and D-max were reduced to 1.78% (p = 0.014), 2.40% (p = 0.236), and 2.81% (p = 0.207), respectively, when the DV-(Upper) gEUD optimization was used compared to DV-base optimization and reduced to 4.76% (p = 0.001), 5.84% (p = 0.001), and 6.91% (p = 0.000), respectively, when using the DV-(Upper+Target) gEUD optimization. Comparing the DV-(Upper) gEUD and the (Upper+Target) gEUD optimization, these values were further reduced to 2.99% (p = 0.022), 3.50% (p = 0.059), and 4.18% (p = 0.049), respectively, when the (Upper+Target) gEUD optimization was used. The DV-gEUD optimization plan showed a better dosimetric profile compared to the DV-based optimization. For HS-WBRT treatment plans using gEUD-based optimization, we recommend that the parameter "a" of the hippocampus be set at 20 and that the gEUD of the OARs and the planning target volume (PTV) be optimized at the same time.