A dosimetric comparison of copper and Cerrobend electron inserts

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Electron beam therapy utilizes aperture inserts for precise dose delivery.
• Lead-alloy (Cerrobend) inserts are standard, but copper inserts are being evaluated for potential benefits.
• Clinical implementation requires understanding dosimetric equivalence and safety.

Purpose of the Study:

• To compare dose distributions between copper and lead-alloy (Cerrobend) aperture inserts in electron beam therapy.
• To determine if copper inserts can be used with commissioning data acquired using lead-alloy inserts.

Main Methods:

• Manufactured 32 combinations of copper and Cerrobend inserts for various field and applicator sizes.
• Measured percent depth-dose and off-axis dose profiles using an electron diode in water.
• Performed gamma analysis (2%/1 mm criteria) for dose distributions at different energies (6-20 MeV) and source-to-surface distances (SSD: 100 and 110 cm).

Main Results:

• 94 out of 96 insert/applicator/energy/SSD combinations met the 2%/1 mm gamma criteria for >99% of points.
• Copper inserts showed reduced bremsstrahlung dose outside the field (up to 2.5% difference at 20 MeV, 100 cm SSD).
• Minor increases in on-field edge dose (up to 1%) and some gamma failures outside the field were observed with copper, primarily at higher energies and specific applicator/field size combinations.

Conclusions:

• Copper inserts demonstrate clinically acceptable dosimetric performance compared to Cerrobend inserts for electron beam therapy.
• Reduced out-of-field dose with copper is a clinically beneficial advantage, minimizing radiation to healthy tissues.
• Copper inserts can be safely used with existing Cerrobend commissioning data for treatment planning and monitor unit calculations.