Radiomicrosphere Therapy for Liver Cancer
Yttrium-90 (Y-90) microsphere radioembolization, known as Selective Internal Radiation Therapy (SIRT), via hepatic arterial administration is a treatment for patients with primary and metastatic liver cancer because the primary blood supply to liver tumors is from the hepatic artery while the majority of the blood supply to the normal liver is from the portal vein. The micro-vascular density of liver tumors is 3-200 times greater than the surrounding liver parenchyma further improving the selectivity of the therapy to the tumor. In this treatment, 30 μm diameter spheres labeled with the radioactive isotope Y-90 (a high-energy beta particle–emitting radioisotope) become lodged in the arterioles within the tumor and destroy the tumor while leaving the normal liver tissue mostly unharmed. For treatment planning Tc-99m-macro aggregated albumin (MAA) is infused into the proper hepatic artery and a perfusion scintigraphy is performed. However, the significant difference in size, shape, and other properties of the MAA and the Y-90 microspheres complicates the treatment planning because the MAA particles cannot be expected to distribute the same as the Y-90 microspheres. Thus it is desirable to develop and use a new biodegradable sphere for accurate SIRT planning. The production and in vitro evaluation of various polymers (PGCD, CHS and CHSg) microspheres for a RMT and RMT planning will be described. For imaging, the particles are labeled with 68Ga or 99mTc. Microparticles with a 30±10 μm size distribution are prepared by emulsion method. The in vitro half-life of the particles is determined in PBS buffer and porcine plasma and their potential application (treatment or treatment planning) established. Studies are also done in rats and mice to determine in vivo labeling stability and microsphere degradation rate. Numerical dosimetry calculations are done to evaluate the radiation field and dose distributions and assure radioprotection standards are met.