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 techniques for the kinetic analysis of these images rely on user selection and drawing of regions to be analyzed. Such analyses do not reveal unexpected kinetic activity outside of the selected regions of interest and do not provide a whole-image assessment regarding the pharmacokinetics of an agent. At Memorial Sloan-Kettering Cancer Center, a method for generating images in which the pixel value represents a kinetic parameter has been developed. This work extends the method into a new application in which whole-body parametric images are used to examine the kinetics of Bi213-HuM195 in patients with leukemia.


METHODS
Bi213-HuM195 is typically administered in multiple injections over 2-4 d, yielding a progressive increase in the amount of antibody administered. Patients are injected with individual doses while positioned in a gamma camera, and imaging is initiated at the start of the injection. The acquisition is performed in dynamic mode with images collected at several time intervals over 1 h. Using software developed in-house, images are corrected for patient movement through iterative alignments, decay corrected, and summed to yield a series of images over regular time intervals. Parametric rate images are obtained by fitting a linear expression to the counts in each pixel. In this study, rate images from a patient's first injection were compared with rate images from the last injection.


RESULTS
The conventional planar images of antibody distribution showed significant uptake in liver, spleen, and marrow, whereas the generated rate images displayed different patterns, sometimes with negative values in liver and spleen and positive values in marrow, reflecting clearance and uptake rates rather than total accumulation. The impact of the progressive increase in antibody administration was observed by comparing the first with the last rate images. Interpatient comparisons were also made and showed that rate image patterns varied depending on patient-specific conditions such as the amount of disease and previous therapies undergone by the patient.


CONCLUSIONS
Rate images make it possible to succinctly display kinetic information about an agent's behavior over the entire acquired image.
Kolbert
K S
KS
Department of Medical Physics Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
Hamacher
K A
KA
Jurcic
J G
JG
Scheinberg
D A
DA
Larson
S M
SM
Sgouros
G
G
D000911:Antibodies, Monoclonal / Q000627:therapeutic use; D001729:Bismuth / Q000627:therapeutic use; D015902:Gamma Cameras; D006801:Humans; D007951:Leukemia, Myeloid / Q000532:radiotherapy*; D016499:Radioimmunotherapy; D011868:Radioisotopes / Q000627:therapeutic use
D000911:Antibodies, Monoclonal; D011868:Radioisotopes; D001729:Bismuth