Parametric images of antibody pharmacokinetics in Bi213-HuM195 therapy of leukemia

Kinetic analysis of gamma camera patient images can provide time-dependent information about antibody behavior. Current region-of-interest-based techn iques for the kinetic analysis of these images rely on user selection and d rawing of regions to be analyzed. Such analyses do not reveal unexpected ki netic activity outside of the selected regions of interest and do not provi de a whole-image assessment regarding the pharmacokinetics of an agent. At Memorial Sloan-Kettering Cancer Center, a method for generating images in w hich the pixel value represents a kinetic parameter has been developed. Thi s work extends the method into a new application in which whole-body parame tric images are used to examine the kinetics of Bi213-HuM195 in patients wi th leukemia. Methods: Bi213-HuM195 is typically administered in multiple in jections over 2-4 d, yielding a progressive increase in the amount of antib ody administered. Patients are injected with individual doses while positio ned in a gamma camera, and imaging is initiated at the start of the injecti on. The acquisition is performed in dynamic mode with images collected at s everal time intervals over 1 h. Using software developed in-house, images a re corrected for patient movement through iterative alignments, decay corre cted, and summed to yield a series of images over regular time intervals. P arametric rate images are obtained by fitting a linear expression to the co unts in each pixel. In this study, rate images from a patient's first injec tion were compared with rate images from the last injection. Results: The c onventional planar images of antibody distribution showed significant uptak e in liver, spleen, and marrow, whereas the generated rate images displayed different pattems, sometimes with negative values in liver and spleen and positive values in marrow, reflecting clearance and uptake rates rather tha n total accumulation. The impact of the progressive increase in antibody ad ministration was observed by comparing the first with the last rate images. Interpatient comparisons were also made and showed that rate image pattern s varied depending on patient-specific conditions such as the amount of dis ease and previous therapies undergone by the patient. Conclusion: Rate imag es make it possible to succinctly display kinetic information about an agen t's behavior over the entire acquired image.