Bone marrow dosimetry in peptide receptor radionuclide therapy with [Lu-177-DOTA0,Tyr3]octreotate

Abstract

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Objectives: Adequate dosimetry is mandatory for effective and safe peptide receptor radionuclide therapy (PRRT). In the past most research focussed on kidney dosimetry. As another potentially dose limiting organ, the bone marrow should not be neglected. Usually the dose to the bone marrow is calculated from the residence time of the radiopeptide in the blood. Since some of the stem cells in the bone marrow express somatostatin receptors, the calculated absorbed dose might be underestimated using this model.

Methods: A bone marrow aspiration was drawn in fifteen patients with metastatic neuroendocrine tumors who underwent treatment with [177Lu-DOTA0,Tyr3]octreotate, 4, 7 or 8 days after the treatment. The activity in the bone marrow was compared with the activity in the blood drawn at the same time. Simultaneously the activity in the remainder of the body was calculated. Assuming the bone marrow being part of the remainder these results were compared to the activity in the bone marrow.

Results: A strong linear correlation between the activity in the bone marrow aspirate and the blood was found (r = 0.914, p<0.001). The slope of the regression line was m = 1.35 indicating slightly higher activities in the blood. No correlation between the activity in the remainder of the body and in the bone marrow aspirate was found (r=0.444, p=0.172).

Conclusions: The high correlation between the activity in the bone marrow aspirate and the blood at different time points and over a range of activities indicates that dosimetry using the activity in the blood to calculate the absorbed dose in the bone marrow is probably adequate. No evidence is found, that due to somatostatin receptor positive cells, higher activity is present in the bone marrow than in the blood because much of the activity in an aspirate is caused by circulating blood. Therefore it can be concluded that most of the absorbed dose in the bone marrow is contributed by the circulating blood.

Research Support (if any): Swiss National Science Foundation Novartis Foundation