Geometry-optimized electron beam scattering foils enabling dose uniformity and dose rate enhancement for FLASH...

Area of Science:

• Medical Physics
• Radiation Oncology
• Accelerator Physics

Background:

• FLASH radiotherapy (FLASH-RT) requires ultra-high dose rate (UHDR) irradiation platforms, which are currently limited in availability.
• Developing compact UHDR systems is essential for advancing FLASH-RT research and clinical applications.

Purpose of the Study:

• To optimize electron scattering foils (SFs) for a compact 6 MeV linear accelerator (linac) at a short source-to-surface distance (SSD).
• To achieve lateral uniform dose delivery with UHDR for FLASH-RT studies using an optimized SF design.
• To enable dose rate modulation for comparative studies between conventional and UHDR radiotherapy.

Main Methods:

• Utilized Geant4 Monte Carlo simulations coupled with the Nelder-Mead simplex algorithm to design optimized aluminum SFs.
• Investigated two geometric strategies: stacked-layer and ring structures for SFs.
• Quantified dose distributions using radiochromic EBT-3 films and modulated linac parameters (anode voltage, pulse width, frequency) to assess dose rate dependencies.

Main Results:

• Achieved uniform integrated lateral dose profiles (<5% flatness) in the first 10 mm of PMMA for a 3.5 cm field at 11 cm SSD using an optimized stacked-layer SF.
• Demonstrated adjustable dose-per-pulse from 0.09 to 8.37 Gy, yielding instantaneous dose rates from 4.25×10^4 to 2.09×10^6 Gy/s.
• Simulations showed potential for <5% flatness for fields up to 10 cm diameter using ring structure SFs.

Conclusions:

• The developed system supports comparative studies of conventional radiotherapy and FLASH-RT effects by operating across both dose rate regimes.
• The study provides a methodology for SF design and UHDR parameter refinement, applicable to compact FLASH platform development.
• This work facilitates the advancement of UHDR irradiation capabilities for FLASH-RT research.