Monitoring 3D dose distributions in proton therapy by reconstruction using an iterative method

The Bragg peak of protons can be determined by measuring prompt γ-rays. In this study, prompt γ-rays detected by single-photon emission computed tomography with a geometrically optimized collimation system were reconstructed by an iterative method. The falloff position by iterative method (52.48 mm) was most similar to the Bragg peak (52 mm) of an 80 MeV proton compared with those of back-projection (54.11 mm) and filtered back-projection (54.91 mm) methods. Iterative method also showed better image performance than other methods.