Experimental facts supporting a red marrow uptake due to radiometal transchelation in 90Y-DOTATOC therapy and...

Area of Science:

• Nuclear Medicine
• Radiopharmaceutical Dosimetry
• Medical Imaging

Background:

• Red marrow (RM) is a critical site for hematopoiesis and a potential target for radiation toxicity from radiopharmaceuticals.
• Understanding RM uptake of diagnostic and therapeutic agents is crucial for accurate dosimetry and predicting toxicity.

Purpose of the Study:

• To evaluate red marrow (RM) uptake of (111)In-diethylenetriaminepentaacetic acid (DTPA)-D-Phe(1)-octreotide and (86)Y-DOTATOC.
• To assess the correlation between RM absorbed doses and platelet count reduction as a measure of biological dose.

Main Methods:

• Retrospective analysis of SPECT and PET imaging data from 12 patients.
• Quantification of RM uptake of radiotracers and calculation of absorbed doses.
• Correlation analysis between RM absorbed doses and platelet count nadir.
• In vitro experiments to investigate radiometal metabolism in plasma.

Main Results:

• Excellent correlation (R=0.80) between RM uptake of both tracers, confirming physiological uptake.
• (86)Y-DOTATOC RM activity kinetics differ from blood and tumors, suggesting non-somatostatin receptor-mediated uptake.
• In vitro studies indicated transchelation of radiometals to transferrin as a potential mechanism for RM uptake.
• A strong correlation (R=0.96) was observed between RM absorbed doses and platelet count reduction in patients without prior chemotherapy.

Conclusions:

• RM uptake of these radiotracers is a genuine physiological process, likely mediated by radiometal transchelation to transferrin.
• RM absorbed dose is a reliable predictor of acute RM toxicity, specifically platelet count reduction.