Dosimetric Validation of Volumetric Modulated Arc Therapy with Three 6MV Beam-Matched Linear Accelerators

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Linear accelerator (LINAC) downtime can disrupt patient radiotherapy schedules.
• Switching treatment plans between LINACs requires identical dosimetric characteristics (beam-matching).
• Beam-matching is crucial for maintaining treatment consistency and avoiding patient inconvenience.

Purpose of the Study:

• To evaluate the clinical significance of beam-matching for Volumetric Modulated Arc Therapy (VMAT) plans.
• To assess dosimetric consistency across different LINAC models.

Main Methods:

• Established baseline dosimetric data using a 6 MV beam from a Clinac 2100CD.
• Factory-tuned two other LINAC models (2300CD, Unique Performance) to match baseline.
• Analyzed Percentage Depth Dose (PDD), beam profiles, output factors, and Multi-Leaf Collimator (MLC) properties.
• Created and compared VMAT plans and point dose measurements for 30 patients (head and neck, thorax, pelvis).

Main Results:

• Excellent energy matching was confirmed by TPR 20/10 for 10x10 cm² fields.
• Point dose measurement deviations were within ±3% across all LINACs.
• Planar dose maps demonstrated >95% passing rate with a gamma (γ) value < 1.

Conclusions:

• Treatment planning system (TPS) modeling confirmed good agreement for 6 MV beams across the three LINACs.
• The evaluated LINACs are clinically interchangeable for VMAT delivery, ensuring treatment continuity.
• Beam-matching is clinically significant for maintaining radiotherapy precision and patient throughput.