| Περίληψη: | Neuroendocrine tumors (NETs) are heterogeneous neoplasms (approximately 5 cases per
100,000) that grow from neuroendocrine cells mainly from the gastrointestinal tract (GEP - NETs) and
rarely in the bronchopulmonary system and can be found in various regions. For their treatment it is
recommended to use [Lu-177] -DOTATATE in 4 sessions administered every 2-3 months. Τhese
treatments should be based on individualized dosimetry with the aim of delivering therapeutically
effective absorbed doses to tumors while maintaining doses in organs at risk (Organs At Risk-OARS)
below the limits of deterministic effects. For the correct and personalized treatment of tumors, the
calibration, acceptance and quality controls of the design system consisting of the hybrid imaging system
SPECT / CT (Single Photon Emission Computed Tomography / Computed Tomography) and the
computer dosing system are necessary. The purpose of this work is to calibrate and accept the treatment
planning system consisting of the SPECT / CT system and the dosing computer system, to determine the
basic reference parameters and their introduction into the software, which leads to a correct calculation
of the absorbed dose. One of these parameters is the calibration factor (calibration factor) and the
sensitivity in the SPECT / CT system, specifically the system volume sensitivity (System Volume
Sensitivity SVS) for the isotope Lu-177.
Methods: The dose calibrator (Atomlab 500, Biodex, USA) was calibrated with a NIST traceable 177Lu
source. The determination of energy and uniformity map on hybrid system SPECT/CT was held with a
point-like source. An evaluation on phantom was performed to determine the SPECT/CT calibration
factor (System Volume Sensitivity, SVS). Then, dosimetry was carried out with dosimetry workstation
(PLANET® Dose) in patients with neuroendocrine tumors after the first and second injection of 7.2 ± 0.2
GBq of [177Lu] Lu-DOTA-TATE. SPECT/CT images were acquired at 4 h, 24 h, 72 h and 192 h postinjection and were reconstructed. To determine the fitting curve, the change of the absorbed dose was
checked through the PLANET® Dose. Finally, to determine the correct threshold during the segmentation
in the functional mode in the tumors, the absorbed doses for 10-90% threshold were recorded.
Results - Conclusions: The dial value for Lu -177 isotope with activity 429 MBq (11.59Ci) in 0.5ml vial
was 115.4. Τhe calibration factor that was decided to be used to the for dosimetry was 51.5 in the specific
clinical department. The absorbed doses to the kidneys were 23.86 Gy (did not exceed 27 Gy) and the
dose to the liver 14.23 Gy (did not exceed 30 Gy). Τhe fitting curves are depicted small variations with
the exception of Χ-exponential. In this project Βi-exponential curve was preferably chosen. Finally, the
threshold decided to be used in dosing was 40%. Due to the lack of literature and the possibility of
comparison, the procedures followed were done both with the help of the manufacturer and after
discussions with other clinical departments. Finally, it is necessary to repeat and verify the
measurements to optimize the whole practice, as it is an important pioneering method for clinical
decision and treatment effectiveness.
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