Pulsed beam monitoring for electron FLASH

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Radiation Detection

Background:

• Advancements in FLASH radiotherapy necessitate beam monitoring devices with high temporal resolution and wide dynamic ranges.
• Ideal detectors must monitor LINAC pulses, withstand extreme doses and dose rates, and provide beam output, energy, and profile information.

Purpose of the Study:

• To design and evaluate two novel detectors for ultra-high dose-rate (UHDR) monitoring: a multilayer nano-structured high-energy-current (HEC3) detector and a segmented flat (S4) detector.
• To explore the properties of HEC3 and S4 detectors for potential integration into a combined future design.

Main Methods:

• A Novalis-TX LINAC was modified to generate a 10 MeV electron-FLASH beam for testing.
• The HEC3 detector (Al-Aero-Ta-Aero-Al layers) and S4 detector (Cu-air-Al layers) were employed for pulse monitoring.
• Beam characterization utilized a photodiode, Gafchromic film, OSLDs, and an Advanced Markus Chamber.

Main Results:

• Electron-FLASH beams exhibited a Gaussian profile with dose rates up to 260 Gy/s (average) and instantaneous rates of 1.8 x 10^5 Gy/s.
• Both HEC3 and S4 detectors recorded individual pulses at 360 Hz with 4 µs pulse width.
• HEC3 demonstrated linear response with dose, MU, pulse count, and dose rate up to 850 Gy/s, showing high-dose functionality. S4 showed linearity with MU and pulse count but lacked dose rate independence.

Conclusions:

• The HEC3 and S4 detectors are capable of monitoring electron-FLASH pulses, serving distinct roles in beam monitoring.
• HEC3 technology is suitable for monitoring high-dose and UHDR beams, offering high temporal resolution for pulse counting.
• A combined HEC3 and S4 design is envisioned for real-time monitoring of temporal structure, spatial profiles, energy, and dosimetric properties of UHDR beams.