This study demonstrates comparable remnant ablation rates in patients prepared for 131I remnant ablation with 3.7 GBq by either administering rhTSH or withholding thyroid hormone. rhTSH-prepared patients maintained a higher quality of life and received less radiation exposure to the blood.

Dosimetry of organs and tumors helps to assess risks and benefit of treatment with Lu-DOTATATE/DOTATOC. However, it is often not performed in clinical routine because of additional efforts, the complexity of data collection and analysis, and the additional burden for the patients. Aiming at a simplification of dosimetry, we analyzed the accuracy of a theoretically substantiated approximation, which allows the calculation of absorbed doses from a single measurement of the abdominal activity distribution. Activity kinetics were retrospectively assessed from planar images in 29 patients with neuroendocrine tumors (NETs; = 21) or meningioma ( = 8) after the administration of Lu-DOTATATE ( = 22) or Lu-DOTATOC ( = 7). Mono- or biexponential functions were fitted to measured data in 54 kidneys, 25 livers, 27 spleens, and 30 NET lesions. It was evaluated for each fit function how well the integral over time was represented by an approximation calculated as the product of the time t of a single measurement, the expected reading at time t, and the factor 2/ln(2). Tissue-specific deviations of the approximation from the time integral were calculated for time points t of 24, 48, 72, 96, 120, and 144 h. The correlation between time integral and approximation improved with increasing time t Pearson r exceeded 0.95 for a t of 96 h or more in all tissues. The lowest maximum errors were observed at a t of 96 h, with deviations of the approximation from the time integral of median +5% (range, -9% to +17%) for kidneys, +6% (range, -7% to +12%) for livers, +8% (range, +2% to +20%) for spleens, and +6% (range, -11% to +16%) for NET lesions. Accuracy was reduced for measurements after 72 or 120 h. For measurements after 24, 48, and 144 h, the approximation led to large deviations for some of the patients, in particular unacceptable underestimates of the absorbed dose to the kidneys. A single quantitative measurement of the abdominal activity concentration by SPECT/CT 4 d after the administration ofLu-DOTATATE/DOTATOC provides a 3-dimensional dose map and can be used to estimate the doses actually absorbed in the treatment cycle with minor additional resources and effort.

The intention is to guide the user through a series of measurements and calculations which the authors consider to be the best and most reproducible way at present.

Chemokine receptor 4 (CXCR4) is a key factor for tumor growth and metastasis in several types of human cancer. Based on promising experiences with a radiolabeled CXCR4 ligand ( 68 Ga-pentixafor) for diagnostic receptor targeting, 177 Lu-and 90 Y-pentixather were recently developed as endoradiotherapeutic vectors. Here, we summarize the first-in-human experience in 3 heavily pretreated patients with intramedullary and extensive extramedullary manifestations of multiple myeloma undergoing CXCR4-directed endoradiotherapy. Methods: CXCR4 target expression was demonstrated by baseline 68 Ga-pentixafor PET. Each treatment was approved by the clinical ethics committee. Pretherapeutic 177 Lu-pentixather dosimetry was performed before 177 Lu-pentixather or 90 Y-pentixather treatment. Subsequently, patients underwent additional chemotherapy and autologous stem cell transplantation for bone marrow rescue. Results: A remarkable therapeutic effect was visualized in 2 patients, who showed a significant reduction in 18 F-FDG uptake. Conclusion: CXCR4-targeted radiotherapy with pentixather appears to be a promising novel treatment option in combination with cytotoxic chemotherapy and autologous stem cell transplantation, especially for patients with advanced multiple myeloma.

The EANM Dosimetry Committee Series "Standard Operational Procedures for Pre-Therapeutic Dosimetry" (SOP) provides advice to scientists and clinicians on how to perform patient-specific absorbed dose assessments. This particular SOP describes how to tailor the therapeutic activity to be administered for radioiodine therapy of benign thyroid diseases such as Graves' disease or hyperthyroidism. Pretherapeutic dosimetry is based on the assessment of the individual (131)I kinetics in the target tissue after the administration of a tracer activity. The present SOP makes proposals on the equipment to be used and guides the user through the measurements. Time schedules for the measurement of the fractional (131)I uptake in the diseased tissue are recommended and it is shown how to calculate from these datasets the therapeutic activity necessary to administer a predefined target dose in the subsequent therapy. Potential sources of error are pointed out and the inherent uncertainties of the procedures depending on the number of measurements are discussed. The theoretical background and the derivation of the listed equations from compartment models of the iodine kinetics are explained in a supplementary file published online only.