Gallium-68 labeled particles: MAA, lactic acid polymer, and SIR-Spheres

Objectives Develop PET imaging products to estimate particle distribution in patients being evaluated for Y-90 microsphere selective internal radiation treatment.

Methods 68Ga-MAA was made according to Even and Green* with some modification. To label the decayed SIR-Spheres, sodium acetate (3 N, 0.3 mL) was added to 14 mCi of Ga-68 generator eluate (5ml, 0.1 N HCl) and mixed with approximately 1.9 million decayed SIR-Spheres for 12 minutes. To label the lactic acid polymer, sodium acetate (3 N, 0.23 mL) was added to 15 mCi of Ga-68 generator eluate (0.1 N HCl, 5 mL), followed by 0.25 mL of 1N NaOH. The mixture was added to polylactic acid microspheres (104 mg, 1-50μm), followed by 0.8 mL of 0.1 N sodium hydroxide. Both products were filtered, rinsed with water, and collected in saline or water. Each tracer (100-300 μCi) was administered intravenously to rabbits. PET scans were performed at 10 min, 1 hr and 2 hr.

Results The process time is reasonable for all three tracers, considering the 68 minute half-life of Ga-68. The radiochemical yields were acceptable, except for 68Ga-lactic acid polymer, which was hindered by the propensity of the polymer to stick to surfaces. The PET scans showed little or no activity visible outside the lungs initially and up to 2 hours post-injection, except for the labeled polymer, in which the inclusion of smaller particles allowed visualization of liver and spleen.

Conclusions All tracers exhibit particle-like behavior, appear stable in vivo for up to 2 hours, and may be useful tools for estimation of SIR-Sphere biodistribution. *Even, Gregory A. and Green, Mark A. Int. J. Appl. Instrum. Part B., 16;319-321; 198

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