Linac mechanic QA using a cylindrical phantom.

Area of Science:

• Medical Physics
• Radiation Oncology
• Imaging Technology

Background:

• Accurate radiation therapy relies on precise linear accelerator (linac) mechanical operation.
• Current linac mechanical quality assurance (QA) methods are time-consuming, limiting their frequency and thoroughness.

Purpose of the Study:

• To develop and validate an automated method for evaluating linac mechanical performance using portal imaging.
• To enable more efficient, thorough, and frequent mechanical QA for improved radiation therapy accuracy.

Main Methods:

• A novel approach using projection portal images of a phantom with radiopaque fiducial markers.
• Marker autodetection incorporated imager response modeling and non-uniform background compensation.
• Linac mechanical parameters estimated via nonlinear multi-objective optimization of marker locations.

Main Results:

• Precise estimation of linac geometry parameters including gantry angle deviation, sag, source-to-axis distance (SAD), source-to-detector distance (SDD), and couch motion.
• Accurate determination of imager shift and orientation parameters.
• High accuracy in marker detection and optimization, with maximum coordinate differences under 0.25 mm.

Conclusions:

• The developed automated procedure offers a more efficient and comprehensive approach to linac mechanical QA.
• This method has the potential to significantly enhance the quality and safety of radiation therapy delivery.
• Implementation of this automated QA will facilitate more frequent mechanical assessments, ensuring optimal linac performance.