Routine individualised patient dosimetry using electronic portal imaging devices

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Electronic Portal Imaging Devices (EPIDs) are crucial for quality assurance in radiotherapy.
• Individualized patient dosimetry requires accurate verification of radiation dose delivery.
• Routine analysis of EPID measurements can enhance treatment accuracy.

Purpose of the Study:

• To analyze routine EPID measurements for individualized patient dosimetry.
• To assess the accuracy of EPID measurements in verifying treatment parameters and machine output.
• To investigate sources of dose delivery errors in radiotherapy.

Main Methods:

• Calibrated camera-based EPIDs were used for central field dose measurements.
• Transit dosimetry was performed by comparing calculated and measured dose data.
• In vivo dose values (D(5)) were back-projected from transit dose measurements and compared to treatment planning system data.
• Dose differences were weighted by monitor units and analyzed over 24 months for ~2500 patients.

Main Results:

• Pre-treatment measurements showed a mean dose difference of 0.0+/-1.7%.
• Patient dosimetry revealed mean transit and D(5) dose differences of -0.7+/-5.2% and -0.3+/-5.6% per session, respectively.
• Identified dose differences were attributed to setup errors, organ motion, density corrections, and anatomical changes.

Conclusions:

• EPIDs are reliable tools for routine verification of treatment parameter transfer and machine output.
• Transit and in vivo dosimetry using EPIDs provide valuable insights into dose delivery error sources.
• Routine EPID analysis supports enhanced patient safety and treatment accuracy in radiotherapy.