A Comprehensive Dosimetric and Plan Quality Evaluation of Non-coplanar VMAT With Flattening Filter-free Versus Flattened Beams for Hippocampal-Avoidance Whole-Brain Radiotherapy: A Multi-Platform Study on Elekta Infinity and UIH uRT-Linac Systems.

IntroductionHippocampal-avoidance whole-brain radiotherapy (HA-WBRT) effectively reduces neurocognitive decline in patients with brain metastases, but evidence from direct multi-platform comparisons remains limited. This study addresses the gap by comparing two mainstream radiotherapy systems for non-coplanar VMAT (NCVMAT) with flattening filter-free (FFF) and flattened (FF) beams.MethodsA retrospective dosimetric cohort study was conducted on 22 consecutive patients. Four plan types were created: MC-NCVMAT (Elekta Infinity/Monaco) FFF/FF and UT-NCVMAT (UIH uRT-linac 506c/uRT-TPOIS) FFF/FF. Dosimetry, organ-at-risk (OAR) sparing, efficiency, and plan quality metric (PQM) were evaluated. Identical constraints were applied across platforms.ResultsUT-NCVMAT showed significantly better homogeneity, conformity, and OAR sparing than MC-NCVMAT. FFF beams outperformed FF in hippocampal protection. UT-NCVMAT reduced beam-on time and planning time by 44%. The 16-item PQM score was significantly higher in the UIH group. Post-hoc power analysis confirmed sample adequacy.ConclusionThe UIH uRT-TPOIS system with NCVMAT FFF may offer superior dosimetry, efficiency, and clinical feasibility for HA-WBRT. The PQM model may serve as a reliable tool for standardized plan evaluation. Further multi-center validation is warranted.