Study on the application of improved VMAT based on collaborative partitioning of beam and target in hippocampus-avoidance whole-brain radiation therapy

To develop an improved linac-based volumetric modulated arc therapy (I-VMAT) for Hippocampus-avoidance whole-brain radiotherapy (HA-WBRT) and compare it with conventional VMAT (C-VMAT) and helical tomotherapy (HT). This retrospective study created HA-WBRT plans (30 Gy/10 fractions) for each of the 24 patients using three different groups: C-VMAT (three full arcs: alternating clockwise with a 15° collimator angle and counter-clockwise with a 345° collimator angle), I-VMAT, and HT. I-VMAT featured PTV and field partitioning based on hippocampus anatomy and a fixed 90° collimator angle. Dosimetric parameters for PTV and organs at risk (OARs), monitor units (MU), and delivery time were compared. Regarding PTV dosimetric parameters (D2 %, D95 %, D98 %, Dmax, Homogeneity Index[HI]), both I-VMAT and HT significantly outperformed C-VMAT (P < 0.05). When including Conformity Index (CI), I-VMAT and HT showed comparable outcomes (P > 0.05). No significant inter-group differences were observed for hippocampus Dmin (P > 0.05). For hippocampus Dmax, I-VMAT (9.89 ± 0.33 Gy) and HT (10.32 ± 0.89 Gy) were superior to C-VMAT (15.50 ± 1.16 Gy) (P < 0.05), with I-VMAT significantly outperforming HT (P < 0.05). Similarly, for hippocampus Dmean, I-VMAT (8.33 ± 0.21 Gy) and HT (8.61 ± 0.37 Gy) yielded significantly lower values than C-VMAT (9.89 ± 0.43 Gy) (P < 0.05), with I-VMAT again superior to HT (P < 0.05). I-VMAT required significantly fewer monitor units (MUs) than C-VMAT (1170.25 ± 62.72 vs. 1346.25 ± 43.76, P < 0.05). Delivery times for I-VMAT (204.80 ± 11.23 s) and C-VMAT (235.76 ± 6.91 s) were significantly shorter than for HT (798.48 ± 22.48 s) (P < 0.05). The I-VMAT technique significantly improved target coverage, dose homogeneity, and hippocampus sparing for HA-WBRT compared to C-VMAT, with metrics outperforming RTOG 0933 criteria. I-VMAT achieved comparable plan quality to HT while offering superior delivery efficiency and lower hippocampus doses.