Estimation of optimal margin for intrafraction movements during frameless brain radiosurgery

Area of Science:

• Medical Physics
• Radiation Oncology
• Neurosurgery

Background:

• Image-guided frameless radiosurgery offers precise tumor targeting.
• Intrafraction patient movement during treatment can compromise dose delivery accuracy.
• Quantifying movement effects is crucial for optimizing treatment margins.

Purpose of the Study:

• To assess the dosimetric impact of intrafraction movements in frameless brain radiosurgery.
• To establish an optimal margin recipe to counteract these movements.

Main Methods:

• Patient movements were tracked using the CyberKnife system's skull-tracking.
• Dosimetric changes were calculated using dynamic-arc plans and dose-grid analysis.
• Optimal margins were derived from statistical analysis of 262 patient datasets.

Main Results:

• A formula (1.0r + 0.2σ) approximates the geometric effect of intrafraction movement.
• Optimal margins of 2.1, 3.2, and 4.2 mm were determined for 90% confidence at 10, 20, and 30 minutes treatment times, respectively.
• A quantitative relationship between dose variation and geometric error was established.

Conclusions:

• A method to quantify dosimetric changes due to intrafraction movement was developed.
• Specific margin recommendations ensure accurate dose delivery in frameless brain radiosurgery.
• This research aids in refining treatment planning for brain radiosurgery patients.