Tumour embolization of the Vx2 rabbit head and neck cancer model with Dextran hydrogel and Holmium-poly(L-lactic acid) microspheres: a radionuclide and histological pilot study

Introduction: Intra-arterial embolization of unresectable malignant tumours with biodegradable microspheres is an effective way of selective anti-tumo ur therapy. Promising candidates are Dextran hydrogel (Dex) microspheres fo r chemo-embolization and Holmium-166 poly(L-lactic acid) ((166)HoPLA) micro spheres for radio-embolization. This study was performed to investigate the distribution of intra-arterially injected microspheres both in vivo and hi stologically in order to establish an optimal size of particles for emboliz ation of head and neck tumours. Material: Twenty rabbits with Vx2 auricular tumours were embolized via the caudal auricular artery with 4 different ba tches of microspheres: Radioactive (166)HoPLA microspheres sieved between 2 0 and 50 mum and Dextran hydrogel microspheres sieved between 20 and 100 mu m (Dex20), 30 and 100 mum (Dex30) or 50 and 100 mum (Dex50). Dex20 and Dex5 0 microspheres were labelled with (99m)Technetium in six cases. Methods: Th e average particle size of the microspheres was determined. The proportion of microspheres entrapped in the tumour was measured with a gamma camera. T he distribution of microspheres around the primary tumour and spill of part icles over into lungs or other or ans was analysed from histological sectio ns. Results: The mean particle diameter varied from 19 to 66 mum: (166)HoPL A 19 +/- 11 mum, Dex20 40 +/- 19 mum, Dex30 50 +/- 19 mum, Dex50 66 +/- 21 mum. The 19 mum (166)HoPLA particles proved inadequate for embolization as 51% spilled over into the lungs, whereas over 95% of the 40-66 mum Dex micr ospheres were retained within the primary tumour area. Particle density in lung tissues proved significantly lower for the Dex50 group. Stray emboli t o the brain occurred in two rabbits. Conclusion: The results of this invest igation show that both Dextran hydrogel and holmium-166 poly(L-lactic acid) microspheres are potential candidates for embolization of head and neck ca ncer. In future studies, arterio-arteriolar anastomoses which might confoun d treatment should be identified and occluded. Particles with a number weig hted mean diameter of at least 40 mum and a volume weighted mean size up to 70 mum should be used. (C) 2001 European Association for Cranio-Maxillofac ial Surgery.