A practical approach for electron monitor unit calculation

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Accurate electron beam data is crucial for calculating monitor units (MU).
• Current methods require extensive measurements, posing a challenge for busy clinics.
• Existing protocols are time-consuming and labor-intensive.

Purpose of the Study:

• To develop a practical method for reducing the volume of electron beam data measurements.
• To maintain the accuracy of monitor unit calculations.
• To optimize data acquisition for clinical electron beam therapy.

Main Methods:

• Investigated dosimetric properties of electron beams, specifically output ratios and effective source-to-surface distance (ESD).
• Utilized a Markus parallel plate ion chamber and a Cardinal Health electrometer for measurements.
• Conducted measurements across various electron energies (5-21 MeV) using three different linear accelerators (Siemens, Varian) in a Plastic Water phantom or water.

Main Results:

• Established that the output ratio of two inserts is independent of the cone used.
• Determined that ESD is a function of field size but independent of cone and jaw opening.
• Demonstrated that these findings allow for a reduction in necessary data points to less than 20% of the original dataset.

Conclusions:

• The proposed approach significantly reduces the time and labor required for electron beam data acquisition.
• The findings support a more efficient and practical method for obtaining essential data for MU calculations.
• This optimization does not compromise the accuracy of clinical dose calculations in radiation therapy.