A multicenter study of modified electron beam output calibration.

Area of Science:

• Medical Physics
• Radiotherapy Dosimetry
• Radiation Oncology

Background:

• Accurate electron beam calibration is crucial for effective radiotherapy.
• Existing protocols like IAEA TRS-398 and AAPM-TG-51 are widely used but may require updates.
• Multicenter studies are essential to assess the generalizability of calibration procedures.

Purpose of the Study:

• To evaluate the accuracy of a modified electron beam calibration procedure.
• To compare the modified calibration against established protocols (IAEA TRS-398 and AAPM-TG-51).
• To assess the performance of the modified calibration across multiple radiotherapy institutions.

Main Methods:

• Utilized Elekta and Varian Linear Accelerators with electron beam energies from 4-22 MeV.
• Employed both cylindrical and parallel-plate ionization chambers for dosimetry measurements.
• Developed a modified calibration using a cylindrical chamber and updated data derived from Monte Carlo calculations.

Main Results:

• The modified calibration demonstrated beam quality conversion factors comparable to TRS-398 and TG-51.
• Dose ratios between the modified calibration and TRS-398/TG-51 showed variations within acceptable clinical ranges.
• The study confirmed the feasibility of the modified calibration across different institutions and equipment.

Conclusions:

• The modified electron beam calibration procedure is accurate and reliable for multicenter radiotherapy.
• Findings support the need to update current calibration protocols with more detailed metrics.
• Emphasis on linac component stability is recommended for future dosimetry protocols.