Target specific collimation within a VMAT trajectory delivery for stereotactic radiosurgery.

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Volumetric modulated arc therapy (VMAT) is standard for stereotactic treatments.
• Single collimator angles in VMAT can be suboptimal for irregularly shaped targets.
• Beam Eye's View (BEV) target shape variations necessitate adaptive planning strategies.

Purpose of the Study:

• To develop and evaluate a VMAT optimization method allowing variable collimator angles within a single arc.
• To improve delivery efficiency, including monitor unit (MU) utilization and beam delivery time.
• To assess the impact of this optimization on treatment plan quality and patient-specific quality assurance (PSQA).

Main Methods:

• Retrospective replanning of 13 stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) cases with irregular targets.
• Segmentation of VMAT arcs to incorporate dynamic collimator angle adjustments based on BEV target shape changes.
• Comparison of optimized plans against original clinical plans using MU, delivery time, PSQA (gamma passing rate), and dosimetric metrics.

Main Results:

• Achieved a 15.1% reduction in MUs while maintaining target coverage.
• Reduced beam-on time by 20% for SRS and 5% for SRT plans.
• Maintained high gamma passing rates (≥99% for 2%/1 mm) and showed no significant differences in dosimetric metrics.

Conclusions:

• The proposed VMAT optimization method enhances delivery efficiency through reduced MUs and shorter treatment times.
• This approach is effective for irregularly shaped targets in SRS and SRT.
• The method maintains plan quality and delivery accuracy, offering a valuable improvement for stereotactic radiotherapy.