Statistical process control analysis for patient-specific IMRT and VMAT QA

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance

Background:

• Patient-specific quality assurance (QA) is crucial for radiotherapy.
• Statistical process control (SPC) offers a framework for evaluating and improving QA processes.

Purpose of the Study:

• To apply SPC to establish control limits for % gamma pass in intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) QA.
• To evaluate the efficiency and capability of IMRT and VMAT QA processes using the process capability index (Cpml).

Main Methods:

• Utilized SPC to analyze % gamma pass data from 278 IMRT and 159 VMAT QA plans.
• Calculated control limits using the first 50 data points and determined Cpml for both IMRT and VMAT QA.
• Employed gamma criteria of 3%/3 mm for QA plan evaluation.

Main Results:

• VMAT QA exhibited higher average % gamma pass (96.7% ± 2.2%) compared to IMRT QA (93.7% ± 3.7%).
• VMAT QA demonstrated lower systematic and random errors than IMRT QA, indicated by higher Cpml values (1.99 for VMAT vs. 1.60 for IMRT).
• Established lower control limits of 85.0% for IMRT and 90.0% for VMAT % gamma pass.

Conclusions:

• The VMAT QA process is more accurate and efficient than the IMRT QA process.
• Both IMRT and VMAT QA processes demonstrate good quality, with Cpml values exceeding 1.0.
• SPC provides a valuable tool for monitoring and ensuring the quality of radiotherapy QA.