Prompt Gamma Timing for range verification with carbon ion irradiation: first experimental measurements and comparison with Geant4 Monte Carlo simulations

TL;DR

This study demonstrates the first experimental application of Prompt Gamma Timing (PGT) in carbon ion therapy, showing strong agreement with Geant4 simulations and potential for real-time range verification.

Contribution

It introduces a dedicated detection system for PGT in carbon ion therapy and validates its effectiveness through experimental measurements and simulations.

Findings

Strong agreement between experimental data and Geant4 simulations within 95% confidence.

Photons are the main contribution to detected signals, especially upstream of the beam.

The system can resolve energy-dependent differences and detect clinically relevant range changes.

Abstract

Prompt Gamma Timing (PGT) is a promising technique for in vivo range verification in particle therapy, exploiting the time-of-flight between primary particles and prompt gamma rays emitted by nuclear interactions. PGT distribution is highly sensitive to beam energy and target density, which, under controlled detector positioning, enables real-time monitoring of particle range, detection of morphological changes, and support for adaptive treatment strategies. This study investigates for the first time the application of PGT in carbon ion therapy. Measurements were performed using a dedicated detection system composed of a silicon strip sensor for primary ion timing and a LaBr3(Ce) read out by a SiPM for secondary radiation. Carbon ion beams with energies of 166.41, 268.86, and 398.84 MeV/u irradiated a homogeneous 30.0 cm PMMA target at CNAO. The secondary radiation detector was positioned at four off-beam positions to assess the robustness of the PGT technique. Simulations based on Geant4 were conducted for all configurations to evaluate agreement and predictive capability. A bin-by-bin comparison of experimental and simulated PGT intensities demonstrated strong agreement within the 95% confidence interval, with no incompatible bins at 166.41 MeV/u, at most 1% at 268.86 MeV/u, and up to 8% at 398.84 MeV/u, depending on detector position. Photons were identified as the dominant contribution to the detected signals, particularly for detector positions upstream with respect to the primary particle beam, minimizing signal contamination from neutrons and charged fragments. The validated experimental-simulation framework confirms the capability of the proposed PGT system to resolve energy-dependent differences and highlights its potential for detecting clinically relevant changes in the particle beam range, supporting further development toward real-time monitoring in carbon ion therapy.