Comparative Analysis of Radiation Dose Reduction in Radiosurgery Versus Whole BrainRadiotherapy for Intracranial Metastases

Objective: To perform a dosimetric comparison between stereotactic radiosurgery and whole-brain radiation therapy, while evaluating plan quality based on conventional indices and a new efficiency index (η50%). Study Design: Comparative studyPlace and Duration of Study: This study was conducted at the Al-Andalus Private Hospital, Iraq from 15th September 2024 to 30th June 2025. Methods: Whole-brain radiation therapy and stereotactic radiosurgery plans were generated for 17 patients using the Monaco Treatment Planning System. Target volumes and critical structures were contoured on fused computed tomography and gadolinium-enhanced magnetic resonance imaging datasets. Dosimetric evaluation included planned target volume coverage, conformity index, homogeneity index, monitor units, organ-at-risk doses, low-dose brain exposure (V10 and V12), gradient index, and efficiency index (η50%). Results: Dose distribution obtained by stereotactic radiosurgery had higher target coverage (99.40% vs 95.98% for whole-brain radiation therapy. Conformity index was better with stereotactic radiosurgery (0.90 vs 0.87), with improved dose homogeneity (0.103 vs 0.126). Stereotactic radiosurgery resulted in higher monitor units (5505.21 vs 305.60). The stereotactic radiosurgery significantly decreased doses to critical organs at risk (p<0.001). Moreover, stereotactic radiosurgery achieved low-dose brain exposure and improved Gradient Index and η50%. Conclusion: The effectiveness of stereotactic radiosurgery in selected patients, allowing a balance between preservation of normal brain tissue and effective local tumor control. The Efficiency Index (η50%) was found to be a useful metric for evaluating dose utilization alongside conventional indices.