Optimizing SRS for Brain Metastases: Understanding the Volume-Gradient Index Relationship

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiosurgery

Background:

• Developing high-quality dosimetric standards for SRS-SRT plans is crucial.
• Key questions involve selecting plan quality metrics, identifying influential factors, and optimizing plan geometry.
• This study focuses on factors influencing plan quality metrics.

Purpose of the Study:

• To establish a framework for generating high-quality SRS-SRT plans.
• To identify key factors influencing plan quality metrics.
• To understand the relationship between target volume and plan quality.

Main Methods:

• Retrospective analysis of 200 SRS-SRT target volumes from two institutions.
• Development of Linear Regression models to assess plan quality metric variability.
• Statistical analysis to identify the most significant regressors.

Main Results:

• Target volume (TV) and multiple targets (MT) were identified as primary influences on plan quality.
• Doubling TV significantly decreases Gradient Index (GI) and moderately increases Gradient Measure (GM).
• The models explained 85% of GI variation and 84% of GM variation.

Conclusions:

• Gradient Index (GI) is a more sensitive metric than Gradient Measure (GM) for small lesions in sub-CC SRS targets.
• Dose per fraction did not significantly affect plan quality metrics.
• Treating multiple targets increases GI and GM, independent of target volume.