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Long-term two-dimensional pixel stability of EPIDs used for regular linear accelerator quality assurance
1School of Mathematical and Physical Sciences, University of Newcastle, Newcastle, NSW 2308, Australia. brian.king@newcastle.edu.au
Australasian Physical & Engineering Sciences in Medicine
|November 1, 2011
Summary
Electronic portal imaging devices (EPIDs) demonstrate high stability over 3 years, justifying annual calibration. This supports advanced dosimetric applications, enhancing clinical efficiency and accuracy in radiation therapy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Imaging Technology
Background:
- Electronic Portal Imaging Devices (EPIDs) are crucial for quality assurance in radiation therapy.
- Current calibration protocols may be more frequent than necessary, impacting clinical workflow.
Purpose of the Study:
- To assess the long-term stability of clinical EPIDs.
- To determine if extended calibration intervals are clinically justifiable.
- To evaluate the feasibility of advanced dosimetric applications using EPIDs.
Main Methods:
- Monthly quality assurance images from three clinical EPIDs were analyzed over approximately 3 years.
- Evaluated EPID positioning system stability, central pixel dose response, and individual pixel stability.
- Compared EPID measurements with ion chamber data.
Main Results:
- EPID positioning stability was excellent (<0.3 pixels variation).
- Central axis dose response tracked ion chamber measurements within 0.5%.
- Mean pixel response variation was ≤0.6%, with >99% of pixels showing <1% variation.
Conclusions:
- Clinical EPIDs exhibit high long-term stability.
- Annual calibration is likely sufficient for most clinical scenarios.
- Enhanced dosimetric use of EPIDs is clinically feasible, improving radiation therapy precision.
