Original Article

MRI-CT Image Fusion in 3D-Conformal Radiotherapy for Glioblastoma: Impact on Target Volume and Eye Dose

Abstract

Purpose: Accurate target delineation is essential for radiotherapy planning in glioblastoma. While CT provides the electron density information required for dose calculation, MRI offers superior soft-tissue contrast and may improve tumor delineation.

Materials and Methods: Computed Tomography (CT) is routinely used for radiotherapy treatment planning; however, Magnetic Resonance Imaging (MRI) provides superior soft-tissue contrast. This study evaluated the improvement of treatment planning in glioblastoma patients by fusing MRI and CT images, with a focus on changes in Clinical Target Volume (CTV) and radiation dose to the eye region. Thirty patients with histologically confirmed glioblastoma underwent both CT and MRI scans. Two plans were generated per patient: MRI–CT fused (dual-modality) and CT-only (single-modality). Demographics, tumor location, CTV, and eye dosimetry (maximum dose, mean dose, D0.03cc, dose–volume histogram metrics) were collected. CT and MRI protocols, registration, and fusion procedures were performed. Statistical comparisons the Wilcoxon signed-rank test, with significance set at P ≤ 0.05 and 95% Confidence Intervals (CI).

Results: Image fusion significantly reduced CTV in both phases (initial: 443.45±190.64 vs 200.19±133.67 cm³; mean difference −243.27 cm³ [95% CI −316.82, −169.71], P<0.001; boost: 265.72±140.72 vs 84.28±57.48 cm³; mean difference −181.44 cm³ [95% CI −232.92, −129.96], P<0.001). Eye doses were consistently lower with fusion: left eye Dmean (initial: −225.06 cGy, P=0.006; boost: −68.05 cGy, P=0.007), left eye Dmax (initial: −620.44 cGy, P=0.010; boost: −142.14 cGy, P=0.015), right eye Dmean (initial: −268.73 cGy, P=0.006; boost: −89.08 cGy, P=0.013), right eye Dmax (initial: −662.06 cGy, P=0.004; boost: −135.52 cGy, P=0.024). Across endpoints, 70–93% of cases favored CT–MRI plans.

Conclusion: In 3D-CRT for glioblastoma, CT–MRI fusion improves anatomical specificity, enabling smaller CTVs and meaningfully lower ocular doses. These findings support routine MRI fusion for safer, more conformal planning. MRI–CT fusion enhances target delineation in glioblastoma but may increase eye dose; careful organ-at-risk sparing is warranted.

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Keywords
Glioblastoma Magnetic Resonance Imaging–Computed Tomography Fusion 3D-Conformal Radiation Therapy Target Volume Ocular Dose Dose Volume Histogram Dose Metrics
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Tizro S, Shabestani Monfared A, Fazilat-Panah D, Nosrati FZ, Jahansouz D. MRI-CT Image Fusion in 3D-Conformal Radiotherapy for Glioblastoma: Impact on Target Volume and Eye Dose. Frontiers Biomed Technol. 2026;.