Ultra-high dose rate dosimetry for pre-clinical experiments with mm-small proton fields

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Ultra-high dose rate (UHDR) proton therapy offers potential advantages for biological effectiveness and treatment efficiency.
• Accurate dosimetry is critical for UHDR proton pencil beam irradiations, especially for small fields.
• Challenges exist in measuring and verifying doses delivered at extremely high dose rates.

Purpose of the Study:

• To characterize an experimental setup for UHDR proton irradiations.
• To evaluate dosimetry challenges in millimetre-small proton pencil beams.
• To identify suitable detectors for real-time dosimetry in UHDR proton pencil beam experiments.

Main Methods:

• Utilized a PSI Gantry 1 setup for proton pencil beam delivery up to ~9000 Gy/s.
• Employed a Faraday cup for measuring proton charge at ultra-high dose rates.
• Characterized transmission ion-chambers and field detectors (EBT3 films, Al2O3:C, PTW microDiamond) against the Faraday cup reference.

Main Results:

• Achieved better than 1% reproducibility in delivered proton charge.
• Identified significant ion-recombination (>30%) in transmission ionization chambers.
• Demonstrated dose rate independence for EBT3 films (±3%), scintillator screens (±1.8%), and PTW microDiamond (±1%).

Conclusions:

• Faraday cups are effective for dose estimation, detector characterization, and on-line verification in UHDR proton experiments.
• The PTW microDiamond is a suitable detector for real-time dosimetry of narrow proton beams up to 2.2 kGy/s.
• Accurate dosimetry is achievable for UHDR proton pencil beams with appropriate detector selection and characterization.