We recently developed the synthesis of ultrasmall gadolinium-based nanoparticles (GBN),
(hydrodynamic diameter <5nm) characterized by a safe behavior after intravenous injection (renal
clearance, preferential accumulation in tumors). Owing to the presence of gadolinium ions, GBN can
be used as contrast agents for magnetic resonance imaging (MRI) and as radiosensitizers. The attempt
to determine the most opportune delay between the intravenous injection of GBN and the irradiation
showed that a very low content of radiosensitizing nanoparticles in the tumor area is sufficient (0.1μg/g
of particles, i.e. 15ppb of gadolinium) for an important increase of the therapeutic effect of irradiation.
Such a promising and unexpected result is assigned to a suited distribution of GBN within the tumor, as
revealed by the X-ray fluorescence (XRF) maps.