Dosimetric Effects of Dynamic Jaw Tracking and Collimator Angle Optimization in Non-Coplanar Cranial Arc Radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Noncoplanar volumetric modulated arc therapy (VMAT) is effective for single cranial targets, sparing normal brain tissue.
• Optimization of VMAT plans can be further enhanced by advanced techniques.

Purpose of the Study:

• To investigate the dosimetric impact of incorporating dynamic jaw tracking and automatic collimator angle selection (CAO) into single-target cranial VMAT plan optimization.
• To compare the efficacy of VMAT plans with and without these advanced features.

Main Methods:

• Twenty-two previously treated cranial VMAT plans were reoptimized with CAO alone, and then with both dynamic jaw tracking and CAO (DJT).
• Target dose conformity was assessed using the Paddick gradient index (GI) and inverse conformity index (ICI).
• Normal brain tissue sparing was evaluated by the volume receiving 5Gy, 10Gy, and 12Gy, normalized to target size.

Main Results:

• Automatic collimator angle selection (CAO) alone showed statistically significant improvement in gradient index (GI) compared to original plans (p=0.03).
• The addition of dynamic jaw tracking to CAO (DJT plans) significantly improved inverse conformity index (ICI) and normal brain metrics (p < 0.01) compared to CAO plans.
• Combined dynamic jaw tracking and CAO resulted in significant improvements across all evaluated metrics (target and normal tissue dose) compared to original plans (p < 0.02).

Conclusions:

• Dynamic jaw tracking and automatic collimator angle selection significantly enhance single-target cranial VMAT plans.
• These techniques improve both target dose distribution and normal tissue sparing, leading to better treatment outcomes.