60 Comparison of organ-based absorbed doses estimations by using PLANET®Dose and OLINDA/EXM V2.0 in patients with peptide receptor radionuclide therapy (PRRT) treated with Lutathera®

Abstract

Introduction Lutathera® [1] have been used to treat patients with neuroendocrine tumors. At the Cancer Research Institute of Montpellier the first patients were treated during 2016. Two software available on the market can be used to compare organ-based absorbed doses, the new version of OLINDA/EXM(OLINDA) V2 [2] within HERMES workstation and PLANET®Dose (PDose) from DOSISOFT. The goal of this work is to compare organ-based absorbed dose estimations by using the local energy deposit approach (LEDA). Methods One female who benefited from Lutathera® was injected with a total activity of 7176.6 MBq [ 177 Lu-[DOTA0,Tyr3]-octreotate. Four SPECT/CT’s were performed using the GE-Discovery NM/CT 670 at 4 h, 24 h, 72 h and 168 h. Dosmetric comparison was for liver, spleen, left and right kidneys. Segmentation and registration were carried on using PDose. Segmentation using the first CT image has been done organ by organ. Rigid registration was performed for each organ using two SPECT/CT’s series and taking the first SPECT/CT as reference. The volume of reference was the same at all time for this dosimetric study and it was used to estimate the mass. PDose provides a bio-kinetics’ analysis tools in which SPECT/CT calibration factors can be entered; bi-exponential fitting was chosen to estimate cumulated activities. Residence times were computed and entered into OLINDA in order to calculate beta-absorbed dose. On the other hand, PDose can establish the absorbed dose by LEDA choosing a bi-exponential fitting function and correcting for tissue density. To allow comparison with OLINDA, the absorbed dose to kidneys was performed weighting the left/right results by the mass. Results Liver, spleen, left and right kidney mass were 1636 g, 99 g, 145 g and 126 g, respectively. Residence times for liver, spleen, left and right kidney were 42.70 h, 0.62 h, 0.78 h, 0.82 h. For liver, spleen and kidneys absorbed dose estimations are 16.0 Gy, 3.9 Gy, 3.7 Gy for PDose and 16.8 Gy, 3.6 Gy, 3.5 Gy for OLINDA, respectively. Relative difference is −4.8%, 8.9% and 5.2% for the same organs. Using OLINDA other organs such as adrenals glands, lungs and pancreas also register absorbed doses. Conclusions Results obtained with PDose using the LEDA hypothesis (with density correction), weighting by the mass, are consistent with OLINDA (with mass correction) in ± 10% for a selected group of organs. This preliminary study should be continued on other organs/tissues of interest in radionuclide therapy.