Real-time prompt gamma monitoring in spot-scanning proton therapy using imaging through a knife-edge-shaped slit

TLDR

The study evaluates a high‑sensitivity imaging system using a knife‑edge slit and position‑sensitive gamma detector for real‑time monitoring of particle‑therapy depth profiles via prompt gamma emissions. Monte Carlo simulations on a head‑sized software phantom were performed to test this concept. The simulations show a clear spatial correlation between high‑energy (>1.5 MeV) gamma rays and prompt gamma emission, negligible neutron background, and sufficient data collected in ~10 ms to locate the distal dose edge with <1 mm accuracy, indicating that simple slit cameras can enable accurate real‑time particle‑therapy adjustment.

Abstract

In this paper we report on Monte Carlo simulations to investigate real-time monitoring of the track depth profile in particle therapy by measuring prompt gamma ray emissions: a high sensitivity imaging system employing a knife-edge-shaped slit combined with a position-sensitive gamma detector was evaluated. Calculations to test this new concept were performed for a head-sized software phantom. Clear spatial correlation is shown between the distribution of gamma rays detected with energies above 1.5 MeV and the distribution of prompt gamma rays emitted from the phantom. The number of neutrons originating from nuclear reactions in the phantom that are detected at these high energies is small. Most importantly it is shown that under common therapy conditions enough data may be collected during one spot-step (of the order of 10 ms) to locate the distal dose edge with a 1σ accuracy of better than 1 mm. This indicates that simple slit cameras have high potential for accurate real-time particle therapy adjustment and may become a practical way to improve particle therapy accuracy.