BEAM MATCHING EVALUATION OF TWO SIMILAR LINEAR ACCELERATORS

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate beam matching in medical linear accelerators (Linacs) is crucial for consistent radiation therapy delivery.
• Siemens Primus Linacs are widely used, necessitating verification of their beam characteristics.

Purpose of the Study:

• To assess the beam-matching consistency between two Siemens Primus Linacs for photon and electron beams.
• To evaluate critical beam parameters including output factors, percentage depth doses, and beam profiles.

Main Methods:

• Comparison of output factor (Sc,p), wedge factor, quality index (TPR20/10), PDD, and beam profiles for 6 and 15 MV photon beams.
• Evaluation of output factor, PDD, and beam profiles for 5, 7, 8, 10, and 12 MeV electron beams.
• Gamma (γ) analysis using 2 mm/2% and 3 mm/3% criteria.

Main Results:

• 6 MV photon beams demonstrated good matching across most field sizes, with exceptions at 4x4 cm².
• 15 MV photon beams showed PDD matching but beam profile discrepancies at larger field sizes under both γ criteria.
• Electron beams met the 3 mm/3% γ criteria for most applicator sizes but failed the stricter 2 mm/2% criteria.

Conclusions:

• The study highlights specific conditions where beam matching is achieved and where it deviates for Siemens Primus Linacs.
• Deviations in beam profiles for 15 MV photons and electron beams under stringent criteria may necessitate adjustments for optimal treatment planning and delivery.