Output calculation of electron therapy at extended SSD using an improved LBR method

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Accurate calculation of output factors is crucial for precise electron beam radiotherapy.
• Existing methods may have limitations for irregularly shaped fields at extended source-to-surface distances (SSD).
• The lateral buildup ratio (LBR) method offers a potential approach for improving these calculations.

Purpose of the Study:

• To generalize the improved LBR method for calculating the output factor (OPF) of irregularly shaped electron beams at extended SSD.
• To validate the accuracy of the generalized LBR method by comparing calculated and measured output factors.

Main Methods:

• Prepared circular and irregular cutouts for electron beam dosimetry.
• Measured percentage depth dose (PDD) and doses at various SSDs using Varian 2100C and ELEKTA Synergy LINACs with different electron energies.
• Calculated lateral spread parameter [σR(z)], effective SSD (SSDeff), and output factors using the LBR method.

Main Results:

• The improved LBR method was successfully generalized for irregularly shaped electron beams at extended SSD.
• Calculated PDD curves and output factors showed good agreement with measured values.
• The percentage difference between calculated and measured output factors was within 2% for clinical SSDs.

Conclusions:

• The generalized LBR method provides accurate output factor calculations for irregularly shaped electron beams at extended SSD.
• This method is applicable across various electron beam energies and LINAC models (Varian 2100C, ELEKTA Synergy).
• The findings support the clinical utility of the improved LBR method in electron beam radiotherapy planning.