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Introduction: Whole-brain radiotherapy (WBRT) remains a key palliative treatment for patients with multiple brain metastases. With advances in image-guided radiotherapy, megavoltage computed tomography (MVCT) from tomotherapy systems has emerged as a potential alternative not only for patient positioning but also for treatment planning. This study evaluates whether MVCT alone can reliably replace conventional kilovoltage CT (kVCT) in WBRT planning and assesses its impact on clinical workflow. Materials and Methods: This retrospective study included 50 patients with multiple brain metastases treated with WBRT (30 Gy in 10 fractions). For each patient, treatment plans were generated using both kVCT and MVCT datasets within the Accuray Precision treatment planning system. Dosimetric comparison was performed using gamma analysis (3%/3 mm criteria), dose–volume histograms, and evaluation of organ-at-risk (OAR) doses. Workflow efficiency was assessed by comparing the time from simulation to treatment initiation. Results: MVCT-based plans showed strong agreement with kVCT plans, with a mean gamma passing rate of 99.7%. Target coverage across all isodose levels was comparable, with no significant differences. OAR doses, including the brainstem, optic structures, and lenses, showed minimal variation and remained within tolerance limits. Notably, MVCT-only planning improved workflow efficiency by eliminating the need for separate CT simulation, enabling faster treatment initiation in urgent cases. Conclusions: MVCT-only WBRT planning using the Radixact system is feasible, accurate, and efficient. It offers a practical advantage in palliative settings by reducing delays and improving patient convenience. Further multicentre studies are needed to confirm these findings. Keywords: MVCT, whole-brain radiotherapy, Radixact, tomotherapy, brain metastases, image-guided radiotherapy, adaptive radiotherapy, dosimetry, workflow efficiency