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

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.