Hippocampal-Avoidance Whole-Brain Radiotherapy: Dosimetric Comparison of 3D-CRT, IMRT, and VMAT for Brain Metastases from Lung Cancer

Background: This study was designed as a dosimetric feasibility analysis to compare hippocampal-avoidance whole-brain radiotherapy (HA-WBRT) using 3D-CRT, IMRT, and VMAT techniques, with particular attention to clinical applicability in resource-limited settings. While 3D-CRT was used as a reference for conventional WBRT, the primary aim was to determine whether IMRT can serve as an effective and accessible alternative to VMAT for HA-WBRT in centers without advanced technology infrastructure. Methods: Fifteen patients undergoing WBRT for symptom relief were planned using 3D-CRT, IMRT, and VMAT on the Elekta Monaco 6.1.4.0 system. Key organs at risk (OARs) such as the optic nerves, chiasm, eyes, and lenses were considered in the treatment planning. Plans were evaluated based on PTV dose distribution, Conformity Index (CI), Homogeneity Index (HI), and OAR dose constraints (RTOG 0933, NRG-CC001). Gamma pass rate analysis (3%/3 mm) was performed for the IMRT and VMAT plans. Results: IMRT and VMAT significantly reduced the hippocampal dose compared to 3D-CRT, with similar PTV coverage and OAR sparing. The mean Dmax for the hippocampus was 15.4 Gy for IMRT and 15.5 Gy for VMAT compared to 31.2 Gy for 3D-CRT. The D100% for the hippocampus was 7.5 Gy for IMRT and 7.6 Gy for VMAT, both well below the RTOG 0933 threshold of 9 Gy, while 3D-CRT delivered 30.3 Gy. Additionally, IMRT and VMAT delivered lower doses to the optic nerves and chiasm. QA results showed gamma pass rates above 96% for all plans. This study focused solely on treatment-planning and dosimetric feasibility without evaluating patient outcomes or clinical follow-up. Conclusions: HA-WBRT with IMRT and VMAT significantly reduced the hippocampal dose while maintaining optimal PTV coverage. VMAT is preferred for its balance of efficacy, protection, and treatment time, while IMRT represents a feasible approach for facilities without VMAT, though it requires stricter dose control and longer treatment times.