[en] A tomographic imaging system for the measurement of the spatial distribution of the absorbed dose during a Boron Neutron Capture Therapy (BNCT) session is presented. The ¹⁰B(n,α)⁷Li boron neutron capture reaction produces a 478 keV gamma ray in 94% of the cases. Therefore its detection can serve as a basis for a non-invasive online absorbed dose determination since the dose absorbed by the tumor and healthy tissue strongly depends on the boron uptake and the neutron flux. For this purpose, a dedicated tomographic imaging system based on Single Photon Emission Computed Tomography is proposed. Monte Carlo numerical simulations are used for the system design aimed to have a spatial resolution of 1 cm. Prototypes based on CdZnTe semiconductor detectors and LaBr₃(Ce) scintillators with optimized shielding were designed with Monte Carlo simulations. They were built and tested in reactor and accelerator based BNCT facilities. A projection of a phantom with two tumors with 400 ppm of ¹⁰B was successfully measured at the accelerator facility of the University of Birmingham. (author)