Technical Note: Unified imaging and robotic couch quality assurance.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Quality Assurance in Radiation Oncology

Background:

• Current quality assurance (QA) for linear accelerator (linac) imaging and robotic couches involves separate, time-consuming procedures.
• Evaluating imaging system alignment requires precise phantom positioning at isocenter.
• Robotic couch QA necessitates initial phantom displacement and subsequent repositioning accuracy checks.

Purpose of the Study:

• To introduce a simplified, integrated quality assurance (QA) procedure for linac imaging components and robotic couch.
• To enhance efficiency by combining imaging and couch QA into a single workflow.
• To develop a custom software module for streamlined QA testing.

Main Methods:

• A custom software module was developed to register a phantom with known shifts to the isocenter.
• Positioning accuracy was measured by comparing the repositioned phantom's location to a CAD model.
• Physical verification was performed using the MV port graticule.
• Software robustness was tested across various kV and CBCT acquisition parameters.

Main Results:

• The integrated QA procedure achieved phantom positioning within 1 mm and 1° SRS tolerances.
• Residual mechanical accuracy errors were minimal (e.g., 0.26 mm vertically, 0.21° pitch).
• The software demonstrated robustness, accurately detecting markers across diverse imaging parameters and agreeing with vendor methods.

Conclusions:

• The proposed QA procedure streamlines workflow compared to traditional two-step methods.
• It effectively accounts for rotational errors in imaging alignment.
• The method simulates a wide range of clinical setup error variations, improving QA accuracy.