Departmental action limits for TQA energy variations defined by means of statistical process control methods

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Helical TomoTherapy systems require robust quality assurance (QA) protocols.
• Monitoring energy output variations is critical for treatment accuracy and patient safety.
• Establishing clear action limits enhances the efficiency of QA processes.

Purpose of the Study:

• To define departmental action limits for energy percentage variation in helical TomoTherapy QA.
• To utilize Statistical Process Control (SPC) techniques for identifying system performance deviations.
• To establish objective criteria for assessing TomoTherapy system operational status.

Main Methods:

• Applied SPC techniques to retrospective quality assurance data from a TomoTherapy system.
• Utilized step-wedge helical TomoTherapy QA module for energy percentage variation measurements.
• Calculated process capability indices (Cp, Cpk, Cpm, Cpmk) using in-control data.

Main Results:

• An action limit of 1.0% for energy percentage variation between measured and reference output signifies optimal TomoTherapy system performance.
• SPC effectively identified out-of-control situations linked to system interventions.
• Cp and Cpk indices were identified as reliable measures of system capability.

Conclusions:

• SPC is an efficient method for establishing departmental action limits for TomoTherapy QA energy measurements.
• The proposed method provides a framework for calculating and reporting action limits for integrated self-checking TQA energy checks.
• Implementing these action limits facilitates corrective improvements in the quality assurance process.