Targeted Radionuclide Therapy: Current status and potentials for future improvements

Purpose: Adequate dosimetry is mandatory for effective and safe peptide receptorradionuclide therapy. The radiation-dose to the bone marrow can be calculated from theresidence time of the radiopeptide in the blood, but it might be underestimated since stemcells express somatostatin-receptors. We verified the blood-method by comparing the resultswith bone marrow aspirations. Also, we compared other models, taking into account theradioactivity in source organs and the remainder of the body. Methods: Bone marrowaspirates were drawn in 15 patients after treatment with[Lu-DOTA,Tyr]octreotate.Radioactivity in the bone marrow was compared with radioactivity in the blood drawnsimultaneously. The nucleated cell fraction was isolated from the bone marrow aspirate andradioactivity was measured. Furthermore, the absorbed dose to the bone marrow wascalculated from the remainder of the body, with and without the additional radioactivity fromsource organs. All results were correlated to the change in platelet counts 6 weeks aftertreatment. Results: Strong linear correlation and high agreement in measured radioactivitiesbetween bone marrow aspirates and blood was found (r=0.914, p<0.001). No correlationbetween any of the calculated absorbed doses and the change in platelets was found. The bestrelation was found for the radioactivity in the nucleated cells of the bone marrow aspirate.Conclusions: There is a high agreement between the radioactivities in the bone marrowaspirate and blood. Neither the models had a significant correlation with the change in plateletcounts. For the prediction of haematological toxicity many other factors may be crucial aswell.