¹⁸ Anniversary Conference 20 Years Cyprus Society Of Nuclear Medicine (CYSNM20) Limassol Cyprus, 6 _th– 10 _th November 2019

Abstract

Objectives: The aim of the study is to provide the first pre- and peri-dosimetry analyses of 177Lu-DOTATATE patients with neuroendocrine tumors receiving higher activities compared to the standard 177Lu-DOTATATE treatment and to compare the results of three different computer codes used for calculating the absorbed dose to the kidneys. In addition, the blood-based and image-based techniques were applied to estimate bone marrow absorbed doses were analyzed to find an optimal way to estimate bone marrow absorbed doses. Methods: Multiple blood samples (up to 96 h), 24 h SPECT/CT data and a series of WB planar images (up to 95 h) were acquired after an administered therapy activity of 14.4 - 19.3 GBq. The administered activities were chosen based on pre-dosimetry kidney absorbed dose coefficients obtained without kidney protection with the aim not to exceed a kidney absorbed dose of 23 Gy after a single administration of 177Lu-DOTATATE (170-237 MBq). Time-activity curves (TAC) and the corresponding time-integrated activity coefficients (TIACs) for kidneys, blood, whole-body and lumbar vertebrae 2-4 (representing bone marrow) were calculated. Based on these data, patient-specific kidney absorbed dose coefficients were obtained with NUKDOS, OLINDA1.1 and IDAC-Dose 2.1. Absorbed doses to the blood were calculated as described by Eberlein et al.[1] Image-based and blood-based bone marrow absorbed doses were analyzed and compared. Results: In blood we observed lower than 8% of the injected activity 2 h after injection (assuming a blood volume of 5.3 liter). Compared to the standard therapy (7.4 GBq) the absorbed dose to the blood after 48 h is higher (mean: 186±54 mGy vs. 79±16 mGy (1)). Image-based (NUKDOS) and blood-based bone marrow absorbed doses ranged from 0.3-0.8 Gy (LV2-4-based) and 0.1-0.3 Gy (blood-based), respectively. After injection of 14.4 - 19.3 GBq 177Lu-DOTATATE, patient-specific kidney absorbed dose coefficients and doses were identical for NUKDOS, OLINDA 1.1 and IDAC-Dose 2.1 and well below 23 Gy (Pat 1: 0.7 Gy/GBq, 9.6 Gy; Pat 2: 0.3 Gy/GBq, 4.8 Gy; Pat 3: 0.4 Gy/GBq, 7.0 Gy). Conclusions: This study provides the first pre- and peri-therapeutic dosimetry data of 177Lu-DOTATATE patients receiving patient-specific higher activities compared to the standard 177Lu-DOTATATE treatment. The results of this study show that high 177Lu-DOTATATE activities can be administered safely based on pre-therapeutic kidney dosimetry. In addition, blood-based bone marrow absorbed doses are by a factor of three lower compared to image-based bone marrow absorbed doses advocating the use of image-based dosimetry. When patient-specific kidney masses are used, OLINDA 1.1 and IDAC-Dose 2.1 provide similar results with NUKDOS which uses patient-specific voxel-based S-values.