Boron Neutron Capture Therapy (BNCT) is a binary radiation therapy which is able to selectively destroy malignant cells while sparing the normal tissue. A 10B containing drug able to target neoplastic cells is administered to the patient which is then irradiated with thermal neutrons that induce the 10B(n,alpha)7Li capture reaction. Therefore BNCT therapy effectiveness is strongly dependent on the ability to induce a high concentration of 10B inside the neoplastic tissue. The correct evaluation of such quantity and of the dose deposited in the tumour is a key element to further enhance BNCT effectiveness. The current methods clinically used to estimate the boron concentration are indirect. To obtain a direct and real-time quantification of the dose delivered to the tumour a BNCT-SPECT system has been proposed. SPECT imaging in BNCT is based on the 478 keV photon emitted in the 94% of the cases due to the 10B thermal neutron capture. To develop a BNCT-SPECT imaging system a CdZnTe (CZT) detector was chosen because it has a high energy resolution and can be employed at room temperature. This study focused on a simulation study of a small 20x20x20 mm3 CZT detector as the base element of the SPECT imaging system. The system was first simulated in an ideal setup using a virtual collimator of 1 mm aperture and a 7 mm spatial resolution was obtained. Then it was modified to obtain more realistic cases using multiple sources. The more realistic cases showed a spatial resolution that could be improved by using a bigger sensitive volume and using smaller angular steps for the data acquisition, but it was still possible to reconstruct the image of the simulated source and to discriminate multiple sources within a phantom. This work showed the capabilities of a small 20x20x20 mm3 CZT detector as a SPECT imager in BNCT and it also showed that with some improvements, a CZT detector can be used as a base for a BNCT-SPECT imaging system.