The use of Theranostic Gadolinium-based Nanoprobes to Improve Radiotherapy Efficacy.

Ultrasmall gadolinium-based nanoparticles (GBN, hydrodynamic diameter < 5 nm) were recently developped. Since they are designed for combining renal clearance, magnetic resonance imaging (MRI) and radiosensitization, these nanoparticles appear as attractive agents for image-guided radiotherapy. Their efficiency to improve the survival time of tumor bearing animals rests on the possibility to determine, from the data collected by MRI, the delay between the irradiation and the intravenous injection of GBN. The attempts to determine this delay were assessed by combining MRT experiments in parallel with MRI and it provided unexpected results. In this talk, we will summarize these results that were achieved through the long term project MD606 (ANR Theraguima) at the ESRF including survival curves of animals as a function of (i) the time delay between injection and irradiation, (ii) the combination between nanoparticles and temozolomide and (iii) the comparison with the radiosensitization issued by the use of Gd chelates instead of GBN. Additionally, the biodistribution of the GBN within the tumor will be presented through MRI results and XRF results (ID21). On going experiments are now focused on the comparison between the efficiency of the GBN using MRT and in parallel a 6MeV irradiator at the local hospital.