Using a 2D detector array for meaningful and efficient linear accelerator beam property validations.

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Medical physicists monitor linear accelerator (LINAC) performance post-commissioning.
• Ongoing assessment of beam properties and impact of repairs is crucial.
• Existing quality assurance methods may require optimization for efficiency and sensitivity.

Purpose of the Study:

• To develop and validate an efficient method for testing critical linear accelerator photon beam properties.
• To establish sensitive constancy tests for detecting beam variations.
• To create a comprehensive test plan for ongoing LINAC quality assurance.

Main Methods:

• Development of a 14-field test plan utilizing a 2D ionization chamber array.
• Identification of critical beam properties including flatness, symmetry, dose, profiles, and ratios.
• Repetition of constancy tests over six weeks to establish investigation levels (± 3 SDs).
• Deliberate introduction of variations in output, penumbra, and energy to assess test sensitivity.
• Testing on a second, distinct LINAC to evaluate method's broader applicability.

Main Results:

• Established investigation levels were significantly tighter than TG-142 annual recommendations.
• Subtle changes in output, beam energy, and penumbra were rapidly identified.
• The test suite successfully differentiated beam properties between two LINACs.
• Validation of beam properties for two photon energies was achievable in approximately 1.5 hours.

Conclusions:

• The 2D ionization chamber array method provides an efficient and sensitive approach to LINAC quality assurance.
• This test plan aids in detecting subtle beam degradations and assessing repair impacts.
• The method supplements existing quality assurance protocols, enhancing machine performance monitoring.