Collision indicator charts for gantry-couch position combinations for Varian linacs

Area of Science:

• Medical Physics
• Radiation Oncology
• Treatment Planning

Background:

• Non-coplanar radiation fields in treatment planning can cause collisions between the gantry, couch, and patient.
• These collisions are often detected late in the planning process or during patient setup, leading to delays and complications.

Purpose of the Study:

• To present a straightforward method for predicting potential collisions during treatment planning with non-coplanar radiation fields.
• To develop easily implementable charts that map safe gantry and couch angle combinations.

Main Methods:

• Created collision avoidance charts using polar graphs plotting gantry and couch angles.
• Collected data by measuring gantry angles that clear couch positions at various vertical and lateral offsets, simulating patient presence with a stereotactic body frame.
• Generated separate charts for different couch angle ranges (0-90° and 270-360°).

Main Results:

• Developed charts displaying allowable gantry and couch angle combinations to prevent collisions.
• Identified regions within the curves as safe, while regions outside indicate a collision risk.
• The method covers common couch positions encountered in patient treatments.

Conclusions:

• The developed charts provide an easy-to-use tool for radiation therapists to quickly assess collision risks.
• Implementation of these charts can reduce planning time, complications, and uncertainties associated with non-coplanar beam arrangements.