98. Patient-specific estimation of the red marrow extracellular fluid fraction for improving the accuracy of red marrow dosimetry in radioimmunotherpy

Abstract

Purpose The red marrow (RM) is the dose-limiting organ in radioimmunotherapy. The RM dosimetry is usually calculated by radioactivity concentrations of blood samples: RM kinetics is derived multiplying the blood kinetics by the “red marrow-to-blood activity concentration ratio” (RMBLR), calculated by patient-specific RM extracellular fluid fraction (RMECFF) and hematocrit (HCT) i.e., RMBLR = RMECFF/(1-HCT) [ [1] Sgouros G. Bone marrow dosimetry for radioimmunotherapy: theoretical considerations. J Nucl Med. 1993; 34: 689-694 PubMed Google Scholar ]. Preliminarily, the possible use of Contrast-Enhanced Magnetic Resonance Imaging (CEMRI) for estimating the patient-specific RMECFF was here investigated. Methods 9 patients (5 men, 4 women) studied with CEMRI for cardiac disorders were examined. Pre- and post-contrast T1 mapping by MOLLI (modified Look-Locker inversion-recovery) sequences was performed, and the extracellular volume fraction (ECV) map was calculated by a novel method - based on a Fast Non-linear Least Squares (FNLS) algorithm. The mean ECV of the spongiosa volume (SV) inside the dorsal vertebra at the heart level was obtained as mean value in a region-of-interest (ROI) lying wholly within the SV. Results The mean ECV of the SV was (mean[range]): 29.9[24.0–35.3]%. Considering the ECV as a preliminary estimation of the RMECFF, and accounting also for the patient HCT values (ranging from 0.340 up to 0.499), the mean RMBLR was 0.430[0.316–0.546], in a good agreement with the range of 0.2–0.4 generally reported in the literature (even though values sometimes well outside this range were also observed) [ [1] Sgouros G. Bone marrow dosimetry for radioimmunotherapy: theoretical considerations. J Nucl Med. 1993; 34: 689-694 PubMed Google Scholar ]. Conclusion The CEMRI is accurate and very promising for patient-specific RMECFF estimations. Accuracy improvements by MOLLI sequence optimisation, or correction for the presence of trabecular bone and fatty tissue into the SV, are currently under investigation. The red marrow (RM) is the dose-limiting organ in radioimmunotherapy. The RM dosimetry is usually calculated by radioactivity concentrations of blood samples: RM kinetics is derived multiplying the blood kinetics by the “red marrow-to-blood activity concentration ratio” (RMBLR), calculated by patient-specific RM extracellular fluid fraction (RMECFF) and hematocrit (HCT) i.e., RMBLR = RMECFF/(1-HCT) [ [1] Sgouros G. Bone marrow dosimetry for radioimmunotherapy: theoretical considerations. J Nucl Med. 1993; 34: 689-694 PubMed Google Scholar ]. Preliminarily, the possible use of Contrast-Enhanced Magnetic Resonance Imaging (CEMRI) for estimating the patient-specific RMECFF was here investigated. 9 patients (5 men, 4 women) studied with CEMRI for cardiac disorders were examined. Pre- and post-contrast T1 mapping by MOLLI (modified Look-Locker inversion-recovery) sequences was performed, and the extracellular volume fraction (ECV) map was calculated by a novel method - based on a Fast Non-linear Least Squares (FNLS) algorithm. The mean ECV of the spongiosa volume (SV) inside the dorsal vertebra at the heart level was obtained as mean value in a region-of-interest (ROI) lying wholly within the SV. The mean ECV of the SV was (mean[range]): 29.9[24.0–35.3]%. Considering the ECV as a preliminary estimation of the RMECFF, and accounting also for the patient HCT values (ranging from 0.340 up to 0.499), the mean RMBLR was 0.430[0.316–0.546], in a good agreement with the range of 0.2–0.4 generally reported in the literature (even though values sometimes well outside this range were also observed) [ [1] Sgouros G. Bone marrow dosimetry for radioimmunotherapy: theoretical considerations. J Nucl Med. 1993; 34: 689-694 PubMed Google Scholar ]. The CEMRI is accurate and very promising for patient-specific RMECFF estimations. Accuracy improvements by MOLLI sequence optimisation, or correction for the presence of trabecular bone and fatty tissue into the SV, are currently under investigation.