Buck, Andreas

Hänscheid, Heribert

Lapa, Constantin

Lassmann, Michael

Werner, Rudolf

Online-Publikations-Server der Universität Würzburg

Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with  177Lu-DOTATATE/-TOC by One-Single Measurement after 96 h   Werner R.A.1,2,3, Lapa C.1,3, Buck A.K.1,3, Lassmann M.1,3, Hänscheid H.1,3  1. Department of Nuclear Medicine, University Hospital Wuerzburg, Wuerzburg, Germany; 2. Johns Hopkins Medical Institution, The Russell H Morgan Department of Radiology and Radiological Science, Division of Nuclear Medicine, Baltimore, United States. 3. European Neuroendocrine Tumor Society (ENETS) Center of Excellence, University Hospital Wuerzburg, Wuerzburg, Germany.          Objectives: Dosimetry of normal organ and tumor tissue of patients envisaged for Endoradiotherapy (ERT) with 177Lu-DOTATATE/-TOC is important to assess risks and benefit of therapy. However, dosimetry is usually not routinely performed because effort and complexity of data collection and analysis. Aiming at a well-founded simplification of dosimetry, we analyzed the accuracy of absorbed dose estimates based on one-single measurement of the activity retention.    Methods: Activity kinetics in 67 kidneys (usually the dose limiting organs in ERT), 30 livers, 34 spleen and 52 tumors were analyzed in patients with repeated planar whole body scans (at least 1-4 h, 1 d, 2 d, and ≥4 d) after 177Lu-DOTATATE/-TOC administration. A bi-exponential decay function was fitted to the data of each evaluable organ/tumor rS and normalized to 100% at its maximum to deduce the relative uptake u(rS,t). This function, after integration over time to deduce the time integrated uptake ũ(rS) and normalization to a high-quality quantitative retention measurement e.g. with a SPECT/CT, can be used to determine the absorbed dose to rS. For a function u(rS,t) decaying mono-exponentially with an effective half-live Teff, ũ(rS) can be approximated by ũ(rS) ≈ ũl(rS,tl) = u(rS,tl) ·tl·2/ln(2) from a single measurement u(rS,tl) at a late time point tl (1). The error is theoretically < 6% if 0.85·Teff < tl < 1.17·Teff. For each uptake function, the values ũl(rS,tl) were calculated from the expected u(rS,tl) at tl = 24 h, 48 h, 72 h, 96 h, 120 h, and 144 h and the deviations from ũ(rS) were determined. The mean tissue specific error was calculated for each time point tl.   Results: For a measurement at tl = 96 h, the deviation of ũl(rS,tl)  from ũ(rS) (figure 1) was determined to be 5% ± 6% (range, -9% to 20%) for kidneys, 7% ± 5% (range, -1% to 20%) for livers, 11% ± 8% (range, 2% to 47%) for spleens, and 2% ± 8% (range, -28% to 16%) for tumors. Accuracy is slightly reduced for measurements after 72 h (kidneys: 9% ± 6%; range, -15% to +25%) or 120 h (kidneys: -5% ± 8%; range, -25% to 8%). Inacceptable underestimates of the absorbed dose to the kidneys are observed for measurements after 24 h (-33% ± 7%; range, -61% to -18%), 48 h (0 ± 8%; range, -33% to 19%), and 144 h (-18% ± 10%; range, -41% to 7%).  For calculating the absorbed dose, assuming a local energy deposition by 177Lu of 0.086 Gy·g/MBq/h, an activity concentration of 1 MBq/g measured in a tumor at 96 h indicates a local absorbed dose of 24 Gy.  Conclusions: A quantitative 3D-image of the abdominal activity concentration distribution in a patient 4 days after the administration of 177Lu-DOTATATE/-TOC is proportional to a map of the absorbed doses to tumors and relevant organs. The proposed method offers a reasonably accurate estimate of the absorbed dose and can be easily implemented to monitor organ and tumor doses in patients with repeated ERT.  Figure 1  Figure 1. Measurement at tl = 96 h, for kidney, liver, spleen, and tumors.  References:  (1) Hänscheid et al. Z Med Phys. 2011 Dec;21(4):250-7. doi: 10.1016/j.zemedi.2011.01.006     Research Support: This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 701983.  This research was originally published in JNM. Werner R.A., Lapa C., Buck A.K., Lassmann M., Hänscheid H.Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with177Lu-DOTATATE/-TOC by One-Single Measurement after 96 h. J Nucl Med May 1, 2017 vol. 58 no. supplement 1:247. © SNMMI. 

Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with  \(^{177}\)Lu-DOTATATE/-TOC by One-Single Measurement after 96 h

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Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with $^{177}$ Lu-DOTATATE/-TOC by One-Single Measurement after 96 h

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Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with 177^{177}177Lu-DOTATATE/-TOC by One-Single Measurement after 96 h

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Less is sometimes more – Accurate Dose Mapping after Endoradiotherapy with $^{177}$ Lu-DOTATATE/-TOC by One-Single Measurement after 96 h