Estimation of LET distributions ofα-particles from measured scintillator-based trajectory images.

Objective. Linear energy transfer (LET) measurements ofα-particles are increasingly important for micro-dosimetric evaluation in targetedα-radionuclide therapy. However, direct LET measurements remain challenging due to the extremely short range ofα-particles in matter. In this study, we propose a method to estimate LET distributions using quenching effects observed inα-particle trajectory images.Approach. α-particle trajectories were imaged using an ultra-high-resolution imaging system consisting of a Gd3Al2Ga3O12scintillator, an optical magnification unit, and an electron-multiplying charge-coupled device camera.α-particles from three radionuclides were measured: Am-241 (5.5 MeV), Po-213 (8.4 MeV) and Po-212 (8.8 MeV). LET distributions were estimated by taking the ratio of simulated dose profiles (without quenching) to measured depth profiles ofα-particle trajectory images (including quenching). The estimated LET distributions were then compared with those obtained from simulations.Main results. The relative LET distributions along the depth direction were successfully estimated from the measured depth profiles for allα-particles with different energies. The estimated relative LET distributions differed from the simulated distributions by no more than 11%-24% over the depth range from 5µm to the Bragg peak position. Approximate absolute LET distributions were also evaluated.Significance. The proposed method enables a simple and effective estimation of LET distributions ofα-particles from measured depth profiles of trajectory images. It is applicable toα-particles with a wide range of energies and has potential for advancing micro-dosimetry in targetedα-radionuclide therapy.