Measuring prompt gamma-ray emissions from elements found in tissue during passive-beam proton therapy

Area of Science:

• Medical Physics
• Nuclear Instrumentation
• Radiotherapy Physics

Background:

• Prompt gamma detection is crucial for proton radiotherapy range verification.
• Existing methods require optimization for both active and passive beam environments.
• High-resolution detectors are needed to accurately measure prompt gamma emissions.

Purpose of the Study:

• To measure prompt gamma rays from various targets using a LaBr3 detector for a passive-scatter proton beam.
• To investigate prompt gamma emission as a function of depth along the beam path.
• To validate the Geant4 Monte Carlo model against experimental results.

Main Methods:

• Utilized a 2″ × 2″ LaBr3 detector to measure prompt gamma rays from water, Perspex, carbon, and liquid-nitrogen targets.
• Performed measurements at various depths relative to the Bragg peak.
• Compared experimental data with simulations from a validated Geant4 Monte Carlo model.

Main Results:

• Prompt gamma peaks were clearly identified for water, Perspex, and graphite targets after reducing background radiation.
• The Geant4 model replicated measured spectra within 10%, with a notable exception for the 4.44 MeV water peak.
• Prompt gamma photopeak profiles correlated with proton dose deposition, predicting range within 8 mm.

Conclusions:

• Prompt gamma detection with LaBr3 detectors shows promise for proton range verification in passive scattering.
• The validated Geant4 model can accurately simulate prompt gamma emissions.
• Depth-resolved prompt gamma measurements correlate well with proton dose and range.