Radioactive holmium acetylacetonate microspheres for interstitial microbrachytherapy: an in vitro and in vivo
Wouter Bult1, Hendrik de Leeuw, Olav M Steinebach
1Department of Radiology and Nuclear Medicine, UMC Utrecht, Utrecht, The Netherlands.
Purpose:
The clinical application of holmium acetylacetonate microspheres (HoAcAcMS) for the intratumoral radionuclide treatment of solid malignancies requires a thorough understanding of their stability. Therefore, an in vitro and an in vivo stability study with HoAcAcMS was conducted.
Methods:
HoAcAcMS, before and after neutron irradiation, were incubated in a phosphate buffer at 37°C for 6 months. The in vitro release of holmium in this buffer after 6 months was 0.5%. Elemental analysis, scanning electron microscopy, infrared spectroscopy and time of flight secondary ion mass spectrometry were performed on the HoAcAcMS.
Results:
After 4 days in buffer the acetylacetonate ligands were replaced by phosphate, without altering the particle size and surface morphology. HoAcAcMS before and after neutron irradiation were administered intratumorally in VX2 tumor-bearing rabbits. No holmium was detected in the faeces, urine, femur and blood. Histological examination of the tumor revealed clusters of intact microspheres amidst necrotic tissue after 30 days.
Conclusion:
HoAcAcMS are stable both in vitro and in vivo and are suitable for intratumoral radionuclide treatment.
