Dose errors due to charge storage in electron irradiated plastic phantoms.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Commercial plastics like PMMA and polystyrene are common in radiation dosimetry.
• These materials act as electrical insulators and can accumulate charge when exposed to electron beams.

Purpose of the Study:

• To investigate the impact of charge buildup in plastic phantoms on radiation dose measurements.
• To highlight the significance of these charging effects in clinical therapy dosimetry.

Main Methods:

• Utilized cylindrical ion chambers embedded in PMMA and polystyrene phantoms.
• Examined dose distribution alterations and reading changes with accumulated electron dose (6-MeV electrons).
• Assessed the influence of various parameters on charge buildup effects.

Main Results:

• Ion chamber readings in plastic phantoms increased with accumulated electron dose, becoming detectable after approximately 20 Gy.
• Charge buildup effects were found to depend on plastic type, phantom dimensions, beam energy, and dose rate.
• Charged phantoms affected subsequent readings in various radiation beams for extended periods.

Conclusions:

• Charge buildup in common plastic phantoms significantly impacts radiation dosimetry accuracy.
• Clinical therapy dosimetry may experience 5-10% errors due to these effects.
• Recommends the adoption of conducting plastic phantoms to mitigate charge accumulation issues.