Contrast-enhanced (CE) T2-fluid-attenuated inversion recovery (T2-FLAIR) and CE T1-weighted imaging(T1WI) are used in the routine clinic to assist radiation oncologists for accurate gross tumor target volume (GTV) delineation of brain metastases (BMs). In our previous study, CE T1WI should be performed ≥ 10 min after contrast agent injection when determining the GTV of large-volume BMs. Furthermore, we demonstrated that a combination of enhancement scans with different delay times is necessary to accurately assess the boundaries of the GTV. However, this approach requires a significant amount of time. Therefore, this prospective study aimed to analyze the imaging effect of delayed CE T2-FLAIR on large-volume BMs and investigate its feasibility for GTV delineation in radiotherapy. A total of 76 patients with BMs (184 lesions) were prospectively enrolled. All patients underwent magnetic resonance (MR) simulation scans. CE T1WI scans were performed 1, 3, 5, 10, 18, and 20 min after gadolinium-based contrast agent injection. CE T2-FLAIR was performed after the 10-min delayed CE T1WI. The BMs GTVs were determined on various sequence images and defined as regions of interest (ROIs), such as ROI−1 min, ROI−3 min… ROI-20 min, and ROI−T2−FLAIR. ROI−1 min, ROI−3 min, ROI−5 min and ROI−T2−FLAIR were merged as the fusion ROI. The fusion of all CE T1WI ROIs (1, 3, 5, 10, 18, and 20 min) was defined as ROI−total, and used as the reference. The signal intensity, volume, and shape of the ROIs were compared. ROI−T2−FLAIR had the highest contrast ratio (0.77 ± 0.39), which was 148.4%, 126.5%, and 126.5% higher than that of ROI−1 min, ROI−3min, and ROI−5 min, respectively. The ROI−T2−FLAIR volume increased by 11.5%, 8.6%, and 6.6% compared to ROI−1 min, ROI−3min, and ROI−5 min volumes, while decreasing by 17.44% compared to ROI−total(P < 0.05). Compared with ROI−total, all fusion ROIs all had volume differences < 0.08 cm3 and increase rates < 5%. Compared with ROI−total, ROI−T2−FLAIRhad the smallest Dice similarity coefficient (DSC); whereas the DSCs of the fusion ROIs were 0.903 to 0.917. The Hausdorff Distance of each ROI was < 3 mm. The combined use of delayed CE T2-FLAIR and CE T1WI may improve visualization of brain metastases and provide additional information to support tumor target delineation.

The application of contrast-enhanced T2-FLAIR MRI in gross tumor target volume determination for radiotherapy of large-volume brain metastases

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2026年7月1日

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Shanshan Du,
Yong Yin,
Rui Liu,
Ruozheng Wang,
Xin Liu,
Guanzhong Gong

摘要

Contrast-enhanced (CE) T2-fluid-attenuated inversion recovery (T2-FLAIR) and CE T1-weighted imaging(T1WI) are used in the routine clinic to assist radiation oncologists for accurate gross tumor target volume (GTV) delineation of brain metastases (BMs). In our previous study, CE T1WI should be performed ≥ 10 min after contrast agent injection when determining the GTV of large-volume BMs. Furthermore, we demonstrated that a combination of enhancement scans with different delay times is necessary to accurately assess the boundaries of the GTV. However, this approach requires a significant amount of time. Therefore, this prospective study aimed to analyze the imaging effect of delayed CE T2-FLAIR on large-volume BMs and investigate its feasibility for GTV delineation in radiotherapy. A total of 76 patients with BMs (184 lesions) were prospectively enrolled. All patients underwent magnetic resonance (MR) simulation scans. CE T1WI scans were performed 1, 3, 5, 10, 18, and 20 min after gadolinium-based contrast agent injection. CE T2-FLAIR was performed after the 10-min delayed CE T1WI. The BMs GTVs were determined on various sequence images and defined as regions of interest (ROIs), such as ROI_−1 min, ROI_−3 min… ROI-_20 min, and ROI_{−T2−FLAIR}. ROI_−1 min, ROI_−3 min, ROI_−5 min and ROI_{−T2−FLAIR} were merged as the fusion ROI. The fusion of all CE T1WI ROIs (1, 3, 5, 10, 18, and 20 min) was defined as ROI_−total, and used as the reference. The signal intensity, volume, and shape of the ROIs were compared. ROI_{−T2−FLAIR} had the highest contrast ratio (0.77 ± 0.39), which was 148.4%, 126.5%, and 126.5% higher than that of ROI_−1 min, ROI_−3min, and ROI_−5 min, respectively. The ROI_{−T2−FLAIR} volume increased by 11.5%, 8.6%, and 6.6% compared to ROI_−1 min, ROI_−3min, and ROI_−5 min volumes, while decreasing by 17.44% compared to ROI_−total(P < 0.05). Compared with ROI_−total, all fusion ROIs all had volume differences < 0.08 cm³ and increase rates < 5%. Compared with ROI_−total, ROI_{−T2−FLAIR}had the smallest Dice similarity coefficient (DSC); whereas the DSCs of the fusion ROIs were 0.903 to 0.917. The Hausdorff Distance of each ROI was < 3 mm. The combined use of delayed CE T2-FLAIR and CE T1WI may improve visualization of brain metastases and provide additional information to support tumor target delineation.