Evaluation of multiple factors affecting normal brain dose in single-isocenter multiple target radiosurgery

Area of Science:

• Radiation Oncology
• Medical Physics
• Neurosurgery

Background:

• Single-isocenter VMAT (volumetric modulated arc therapy) enables complex radiosurgery for multiple targets.
• Optimizing dose distribution to minimize normal brain exposure is critical in stereotactic radiosurgery (SRS).
• Understanding the impact of planning parameters on dose spillage is essential for treatment quality.

Purpose of the Study:

• To evaluate the influence of various planning factors on normal brain dose in single-isocenter VMAT SRS.
• To determine the most effective strategies for reducing low-dose radiation to healthy brain tissue.
• To assess the role of objective function constraints in dose optimization.

Main Methods:

• Retrospective planning of 10 patients using single-isocenter VMAT SRS.
• Systematic evaluation of 16 planning combinations, including arc numbers, collimator angles, jaw tracking, and mean dose objectives.
• Analysis of normal brain dose, specifically low-dose spill, and target coverage.

Main Results:

• Incorporating a 2 Gy mean dose objective for healthy brain significantly reduced low-dose spill.
• Jaw tracking and optimized collimator angle selection also decreased low-dose volume, but to a lesser extent.
• Target coverage remained unaffected by the inclusion of normal brain dose constraints.

Conclusions:

• A mean dose limit for normal brain in the objective function is crucial for minimizing low-dose spill in single-isocenter VMAT SRS.
• Planning techniques like jaw tracking and collimator angle optimization contribute to dose reduction.
• This study highlights the importance of including relevant quality metrics in the objective function for comparing inverse-planned treatment techniques.