2D dosimetry in a proton beam with a scintillating GEM detector

Area of Science:

• Medical Physics
• Radiation Detection
• Particle Therapy

Background:

• Particle therapy requires precise pre-treatment verification of dose distributions.
• Scintillating gas detectors offer a potential solution for 2D dosimetry.
• Gas Electron Multipliers (GEM) enhance gas multiplication for photon emission detection.

Purpose of the Study:

• To characterize a novel 2D position-sensitive dosimetry system using a scintillating gas detector with GEM structures.
• To evaluate the detector's performance for relative dose measurements in particle therapy.
• To assess key properties including response reproducibility, dose and dose rate dependence, and spatial/temporal response.

Main Methods:

• Development of a dosimetry system using an Ar/CF(4) scintillating gas mixture and dual GEM structures.
• Detection of emitted photons using a mirror-lens-CCD camera system.
• Characterization experiments conducted using a 150 MeV proton beam, evaluating response stability, linearity, dose rate, field size, and temporal/spatial resolution.

Main Results:

• The detector demonstrated high stability with successive measurements (sigma = 0.6%) and good reproducibility over 2 days (approx. 5%).
• A linear dose response was observed in the range of 0.05-19 Gy.
• No significant dose rate effects were found within tested ranges, and no field size effects were observed for areas between 120-3850 mm(2). A spatial response of <= 1 mm and a signal rise/fall time of 2 microseconds were measured.

Conclusions:

• The scintillating GEM detector is a promising tool for 2D dose distribution verification in particle therapy.
• Its characterized properties, including stability, linearity, and spatial resolution, meet the requirements for precise dosimetry.
• The system's performance indicates its suitability for real-time or near-real-time pre-treatment dose verification.