Distribution of holmium-166 acetylacetonate microspheres after intratumoral injection in a rabbit VX-2 tumour model. A pilot study.

Abstract

In order to optimize and standardize 166HoAcAcMS microbrachy therapy, more insight is needed in the distribution of 166HoAcAcMS after intratumoral injection. For that reason, a pilot was conducted to investigate the distribution patterns of the 166HoAcAcMS after intratumoral injection in VX-2 Tumour bearing rabbits and the feasibility of using in vivo Multimodality imaging for this purpose. 3 NZW rabbits were used for this purpose and supplied with a VX-2 tumour on both hindpaws yielding 4 usable tumours. The animals were randomly assigned to receive either 1,3 or 6 injections intratumorally. The amount of injected activity and corresponding weight in 166HoAcAcMS varied between 10.5-36.3 (MBq) and 1.56-5.40 (mg) respectively. Multimodal imaging (MRI, CT, SPECT) was performed on day -2, 0, 5 and 9. Qualitative visual analysis revealed a heterogeneous HoAcAcMS distribution in all tumours. Also HoAcAcMS patterns could be recognised and included, string and funnel like formations, dense depots, and interconnected HoAcAcMS filled pathways. No substantial visual pattern change in HoAcAcMS was observed between the MRI images of day 0,5 and 9. Finally, the HoAcAcMS tumour coverage for 1, 3, 6 injection sites shortly after treatment (day 0) was calculated to be 33.9%, 57.4%, 11.6% respectively. In conclusion, multimodality imaging for the purpose of investigating in vivo distribution of 166HoAcAcMS after intratumoral injection is feasible and optimising the scan protocols for a larger experimental set-up should be a priority.