Feasibility of MR-guided needle-directed intratumoral HoMS delivery for localized radiation therapy in a large tumor model

Radioablation by direct intratumoral administration of paramagnetic and radioactive holmium microspheres (166HoMS; 10-20μm diameter) is a promising
treatment option for solid, unresectable tumors, especially in areas where the preservation of surrounding tissue and function is essential.
In this study, we demonstrated the feasibility of MR-guided needle-directed intratumoral 165HoMS delivery in a large tumor model (Vx2 rabbit carcinoma).
165HoMS injections were performed using titanium needles under MRI-guidance, facilitated by dynamic 2D dual-plane free induction decay (FID) sampling, allowing for dynamic visualization of 165HoMS delivery and coRASOR reconstructions to highlight the needles with positive contrast. After 165HoMS administration, spatial distribution was investigated using 3D multi-echo gradient echo sequences.
MRI facilitated tumor visualization, entry point determination and needle trajectory planning. The presented approach enabled dynamic monitoring of the needle insertion and needle tip positioning in the tumor, allowing intraprocedural optimization of HoMS delivery. As coRASOR reconstruction demonstrated improved needle visualization with high spatial and temporal resolution; its prospective implementation currently has high priority.