Commissioning and acceptance of planet-onco-dose dosimetric software used for patients undergoing [Lu-177] Lu-dotatate therapy

• Κύριος συγγραφέας: Γιαγτζή, Σμαραγδή
• Άλλοι συγγραφείς: Giagtzi, Smaragdi
• Γλώσσα: English
• Έκδοση: 2022
• Θέματα: Dosimetry; SPECT systems; Nuclear medicine; Δοσιμετρία

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.