Optimizing MRI Protocols for Brain Radiosurgery: The Role of Sequence and Contrast Agent Timing.

Area of Science:

• Radiology
• Radiation Oncology
• Medical Imaging

Background:

• Accurate delineation of brain metastases is critical for effective stereotactic radiotherapy (SRT).
• MRI sequence selection and contrast timing significantly influence apparent lesion volumes.
• Optimizing MRI protocols is essential for precise radiation therapy planning.

Purpose of the Study:

• To systematically investigate the impact of MRI sequence choice and post-contrast timing on brain metastases volume.
• To optimize MRI protocols for accurate target volume delineation in SRT planning.

Main Methods:

• 49 patients with 414 brain metastases were randomized into 6 groups with varying MRI sequences (MPRAGE, SPACE, VIBE) and post-contrast times.
• Lesion volumes were assessed by radiology and radiation oncology specialists.
• Statistical analysis included t tests, ANOVA, and multiple linear regression to evaluate sequence and timing effects.

Main Results:

• Both MRI sequence and contrast timing significantly affected measured lesion volumes.
• SPACE and VIBE sequences yielded larger volumes than MPRAGE, with increasing volumes over time post-contrast.
• Smaller lesions (<1 cm3) exhibited greater relative volume differences due to border variations.

Conclusions:

• MRI sequence and contrast timing are significant factors in brain metastases volume assessment for SRT.
• While SPACE and VIBE improve detection, they can increase border ambiguity and inter-rater variability.
• Standardizing MRI protocols is vital for accurate delineation, reduced toxicity, and improved SRT outcomes.