A strategy to determine off-axis dosimetric leaf gap using OSLD and EPID.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate measurement of the dosimetric leaf gap (DLG) is crucial for radiotherapy precision.
• Traditional methods for DLG measurement can be complex and time-consuming.

Purpose of the Study:

• To assess the dosimetric feasibility of using optically stimulated luminescence dosimeters (OSLD) and electronic portal imaging devices (EPID) for DLG measurements.
• To compare OSLD and EPID-based DLG measurements with ionization chamber dosimetry (ICD).

Main Methods:

• Utilized a Clinac 2100C/D linear accelerator with a Millennium-120 multileaf collimator (MLC).
• Measured DLG at central axis (CAX) and off-axis (OAX) positions using OSLD (DLG_OSLD) and validated with ICD (DLG_ICD).
• Generated a 2D DLG map (2D DLG_EPID) from portal images using custom software with correction factors.

Main Results:

• DLG_OSLD and DLG_ICD showed similar variations at CAX and OAX positions.
• DLG_EPID values agreed with DLG_OSLD and DLG_ICD when using aperture-specific corrections.
• The 2D DLG_EPID map revealed varying DLG patterns for each leaf pair across the field.

Conclusions:

• OSLDs are effective and validated dosimeters for DLG measurements, showing agreement with ionization chamber dosimetry.
• The 2D DLG_EPID map offers a novel approach for modeling leaf-end transmission and commissioning treatment planning systems.