Internal dosimetry and biodistribution of indigenously prepared 177 Lu-DOTA-rituximab in lymphoma and other hematological malignancies treated with rituximab.

Objective: The aim of this study was to evaluate the biodistribution and dosimetry of lutetium-177-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid ( 177 Lu-DOTA)-rituximab in CD20 + non-Hodgkin's lymphoma and other hematological malignancies treated with rituximab.

Methods: The standard dosimetry protocol was used, with cold rituximab infusion, then a diagnostic activity of 177 Lu-DOTA-rituximab. Planar images were acquired at multiple time points. Normal organs and tumor dosimetry were performed by using organ and tumor-specific regions of interest and whole-body counts were obtained serially after pixel matched, background, scatter, and attenuation correction. The mean radiation absorbed doses were obtained from OLINDA/EXM v2.1.1 and ORIGIN software.

Results: A total of 22 patients were included in this study. Prolonged blood pool clearance of 177 Lu-DOTA-rituximab with long residence time in the blood pool and normal organs were observed. The whole body effective half-life was 104.5 ± 22 h. The mean total body radiation absorbed dose was 0.208 ± 0.03 mGy/MBq and the mean total body effective dose was 0.196 ± 0.05 mGy/MBq of 177 Lu-DOTA-rituximab. The mean radiation absorbed doses of 0.613 ± 0.21, 1.68 ± 2, 1.01 ± 0.42, and 0.136 ± 0.02mGy/MBq were seen for the liver, spleen, kidneys, and bone marrow, respectively. Tumor lesion uptake was noticed in two patients with tumor radiation absorbed doses were 0.842 mGy/MBq in one and 9.9 mGy/MBq in the other patient. A strong correlation was obtained between the cumulative activities of radiation-absorbed doses derived from ORIGIN and OLINDA software methods at a significant P value less than 0.001.

Conclusion: The results of our study demonstrated favorable biodistribution and dosimetry of indigenously produced 177 Lu-DOTA-rituximab in patients with CD20 + lymphoma. These results can be used for future studies of radioimmunotherapy employing 177 Lu-DOTA-rituximab.