Correlation functions for Elekta aSi EPIDs used as transit dosimeter for open fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• In-vivo dosimetry is crucial for accurate radiotherapy but often complex and time-consuming.
• Electronic portal imaging devices (EPIDs) offer a promising alternative, avoiding manual detector placement.
• Recent advancements in Elekta aSi EPIDs show potential for transit in-vivo dosimetry with various photon beams.

Purpose of the Study:

• To implement a generalized procedure for transit in-vivo dosimetry using EPIDs.
• To simplify the process by reducing the need for extensive phantom measurements.
• To validate the accuracy of EPID-based dosimetry against treatment planning systems.

Main Methods:

• Developed a method using correlation functions based on EPID transit signals and phantom midplane dose.
• Utilized ratios of transit signals to account for variations in scattered photon contributions.
• Generalized the procedure using data from nine Elekta Precise linear accelerator beams.

Main Results:

• The generalized correlation functions were successfully implemented across multiple Elekta Precise linacs.
• The procedure eliminates the need for solid water equivalent phantom measurements for implementation.
• Reconstructed isocenter doses showed agreement with treatment planning system calculations within a tolerance of ±5% to ±6%.

Conclusions:

• The developed EPID transit dosimetry procedure is efficient and accurate for clinical implementation.
• This method simplifies in-vivo dosimetry, making it more accessible in radiotherapy departments.
• The findings support the routine use of EPIDs for patient-specific dose verification in radiation therapy.