SU-E-J-160: 4D Dynamic Arc of Non-Modulated Variable-Dose-Rate Fields for Lung SBRT: A Feasibility Study

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Static gantry angle Stereotactic Body Radiation Therapy (SBRT) for lung cancer offers dosimetric advantages.
• Motion tracking in SBRT is beneficial for reduced target margins and precise tracking without intensity modulation.

Purpose of the Study:

• To demonstrate that delivering target tracking during gantry rotation can significantly improve delivery efficiency.
• To show that this improved efficiency does not negatively affect plan quality in lung cancer SBRT.

Main Methods:

• A static lung SBRT plan was converted to a 4D arc plan using segment aperture morphing (SAM) to account for target motion and shape changes.
• The 4D plan utilized a variable dose rate and merged segments into a single arc for delivery.
• Delivery time was measured and compared to the planned time.

Main Results:

• The 4D arc plan showed minimal difference in dose distribution compared to the static 3D plan.
• The delivered treatment time for the 4D arc plan was comparable to the static 3D plan, with a 12 Gy treatment taking under 2.5 minutes.
• The delivery efficiency was significantly improved while maintaining plan quality.

Conclusions:

• A novel 4D delivery method converting 3D SBRT plans to 4D arc delivery is feasible.
• This method enhances delivery efficiency, crucial for maintaining accurate target-breathing surrogate relationships during treatment.
• The approach offers benefits of target tracking alongside improved treatment speed.