Prompt gamma spectroscopy of metallic implants in proton therapy

The use of implanted markers for proton range verification has recently attracted increasing attention. This study investigates the feasibility of using prompt gamma (PG) emissions from metallic markers (aluminum, titanium, and silver) for proton range verification in proton therapy. Spectroscopic analysis of PG emissions was performed using a high-purity germanium (HPGe) detector, focusing on the Bragg peak region. Experimental results were validated against GATE/GEANT4 Monte Carlo simulations employing Binary Intranuclear Cascade (BIC) and Liège Intranuclear Cascade (INCL++) models. Distinct PG spectral lines were identified for aluminum (416, 440, 1368, 1810 keV), titanium (159, 889, 983, 1312 keV), and silver (633, 861, 875 keV). Both BIC and INCL++ hadronic models demonstrated consistent distribution patterns in the distal fall-off region, with silver and aluminum showing excellent concordance between experimental and simulated data. Although PG measurements from titanium showed 1–4 mm discrepancies in the distal fall-off region at 889 and 1312 keV, the overall depth-dependent profiles remained consistent. The results demonstrate that metal-generated PG signals are reliably detectable and suitable for proton range verification. This study represents the first experimental validation of PG depth distribution analysis for these metals, highlighting silver's exceptional signal-to-noise ratio at 633 keV and underscoring the potential for practical implementation in proton therapy range verification using high-resolution spectroscopic detection without complex collimation systems.