@article{QIMS155644,
author = {Shan Ren and Jinrong He and Sheng Han and Nuo Xu and Wenyang Wang and Shipai Zhu and An Li and Shoupeng Liu and Jialu Lai and Xiaodong Peng and Renming Zhong},
title = {Impact of field number and monitor units per segment on magnetic resonance-guided hypofractionated stereotactic radiotherapy for brain metastases: plan quality, deliverability, and robustness trade-offs},
journal = {Quantitative Imaging in Medicine and Surgery},
volume = {16},
number = {7},
year = {2026},
keywords = {},
abstract = {Background: Magnetic resonance-guided linear accelerators (MR-Linacs) have recently been introduced for radiotherapy of brain metastases (BMs), including hypofractionated stereotactic radiotherapy (HSRT). However, optimal strategies for planning HSRT within MR-guided adaptive workflows remain to be established. This study aimed to evaluate the influence of field number and minimum monitor unit per segment (MU/segment) on plan quality, and robustness of dose calculations in MR-guided HSRT for patients with solitary medium-sized BMs.Methods: This retrospective study included 20 patients who underwent HSRT for solitary medium-sized BMs, receiving a prescription dose of 30 Gy in three fractions. Four intensity-modulated radiotherapy (IMRT) plans were systematically generated for each patient by varying the number of fields (9 vs. 15) and minimum MU/segment (15 vs. 5): 9FL-IMRT (9 fields, 15 MU/segment), 9FS-IMRT (9 fields, 5 MU/segment), 15FL-IMRT (15 fields, 15 MU/segment), and 15FS-IMRT (15 fields, 5 MU/segment). Plan quality, treatment efficiency, and delivery accuracy were assessed based on dose distributions optimized using structure-based bulk electron density assignment, with patient-specific quality assurance (QA) evaluated via global gamma passing rate (GPR) using 3%/2 mm, 2%/2 mm, and 2%/1 mm criteria. To assess robustness against density-related spatial uncertainties, each plan was reoptimized after simulating skull misalignment with random translational offsets within ±2 mm. These reoptimized plans were recalculated on original computed tomography (CT) datasets using voxel-based electron density as the reference standard. Robustness was quantified by comparing dose distributions between bulk density-based and voxel-based recalculations through GPR analysis using 3%/2 mm, 2%/2 mm, 2%/1 mm, and 1%/1 mm criteria.Results: All four IMRT configurations provided clinically acceptable plans with similar target coverage and no significant differences in conformity, gradient, or homogeneity indices (all P>0.05). Although some dose parameters for normal brain tissue reached statistical significance (overall P},
issn = {2223-4306}, url = {https://qims.amegroups.org/article/view/155644}
}