SU-E-T-448: Switch Patients between Collimation Systems for CyberKnife Treatment Feasibility Study.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiosurgery Technology

Background:

• The CyberKnife system utilizes two collimation systems: the flexible Iris collimator and the fixed cone collimator.
• Iris collimator failures can lead to treatment delays; evaluating system interchangeability is crucial.

Purpose of the Study:

• To assess the feasibility of switching between Iris and fixed cone collimators without requiring treatment replanning.
• To determine if dose distributions remain comparable when switching collimation systems.

Main Methods:

• Monte Carlo simulations were performed on 10 clinical cases comparing Iris and fixed cone collimator plans.
• Key metrics analyzed included conformality index (CI), target volume coverage, and doses to critical structures.

Main Results:

• Initial simulations showed minor dose differences (1-6% higher for fixed plans) and slightly different CIs.
• Adjusting Iris collimator size with a 1.024 scale factor significantly improved dose matching.
• Post-adjustment, target dose differences were <2%, and CIs were nearly identical.

Conclusions:

• Small dose variations between collimation systems can be compensated by adjusting Iris collimator size.
• Dose differences to critical structures were clinically insignificant.
• Patients can be safely switched between Iris and fixed cone collimators without replanning after adjustments and system re-commissioning.