PT - JOURNAL ARTICLE AU - ALEXANDRE, CHICHEPORTICHE AU - Sason, Moshe AU - Krausz, Yodphat AU - GODEFROY, JEREMY AU - Grozinsky-Glasberg, Simona AU - Oleinikov, Kira AU - Gross, David J. AU - Ben-Haim, Simona TI - <strong>Can absorbed doses by organs and tumors after PRRT be predicted from the pre-therapeutic 68Ga-DOTATATE PET/CT study?</strong> DP - 2022 Aug 01 TA - Journal of Nuclear Medicine PG - 2213--2213 VI - 63 IP - supplement 2 4099 - http://jnm.snmjournals.org/content/63/supplement_2/2213.short 4100 - http://jnm.snmjournals.org/content/63/supplement_2/2213.full SO - J Nucl Med2022 Aug 01; 63 AB - 2213 Introduction: After each cycle of Peptide Receptor Radionuclide Therapy (PRRT), dosimetry is performed from quantitative SPECT/CT data (standard protocol), enabling calculation of the absorbed dose (AD) by normal organs and tumors. In our center, dosimetry is used to tune the number of PRRT cycles that a given patient can receive by ensuring that the expected AD will not exceed pre-defined safety thresholds for kidneys and bone marrow. Prediction of AD after PRRT from the pre-therapeutic imaging may enable a more personalized PRRT approach by ensuring safety and efficacy. The aim of the present study was to assess the feasibility of obtaining 177Lu-DOTATATE absorbed dose by organs and tumors after the first PRRT treatment cycle from the pre-therapeutic 68Ga-DOTATATE PET/CT.Methods: Twenty-four consecutive patients who underwent pre-therapeutic 68Ga-DOTA PET/CT followed by PRRT were included in this retrospective study. The 68Ga-DOTA PET/CT data (kidneys, spleen, liver and tumors uptake, injected activity…) were used as independent variables while the 177Lu-DOTA data (kidneys, spleen and tumors uptake or AD) were determined as the dependent variables. Three different approaches were investigated in order to assess the correlation between the PET/CT data and the AD by kidneys, spleen and tumors after the first PRRT cycle. In Method 1, the correlation between the 177Lu-DOTA AD by a given organ/tumor and the corresponding 68Ga-DOTA SUVmeanfor the same organ/tumor was assessed. In the second and third methods, the 68Ga-DOTA radioactivity uptake concentration (kBq/mL) was used as independent variable instead of the SUV. The 68Ga uptake concentration was corrected for decay to the injection time and was normalized by the injected activity, 68Gau0. Method 2 focused on the correlation between the 177Lu-DOTA AD by given tumor/organ and the corresponding 68Gau0 for the same tumor/organ. Method 3 aimed to predict first the normalized 177Lu-DOTA uptake concentration at the PRRT injection time for a given tumor/organ, namely 177Luu0, from 68Gau0. Consequently, a multiple linear regression (MLR) model that was trained on 200 other studies (1) was applied to predict the AD from the predicted 177Luu0. The standard and predicted AD were compared for the different methods using the coefficient of determination r2.Results: The coefficients of determination r2 on the test population between the AD after the first cycle calculated using the standard protocol and the predicted AD from 68Ga-DOTA PET/CT data were 0.03, 0.49 and 0.55 for kidneys, 0.07, 0.69 and 0.83 for spleen and 0.16, 0.70 and 0.67 for tumors, using methods 1, 2 or 3, respectively. Predicted absorbed doses using method 3 had a mean relative difference from the standard values of -4.4% ± 32.3% for kidneys, 7.4% ± 19.2% for spleen, 15.8% ± 52.4% for tumors and a correlation Pearson’s r of 0.97, 0.98 and 0.93, respectively.Conclusions: Predictive dosimetry results using 68Ga-DOTA PET/CT data seems to be feasible but with relative high deviations from QSPECT/CT dosimetry. Best results were obtained with Method 3. Additional studies will assess if advanced statistical models can improve the precision of predictive dosimetry. 1. Chicheportiche A, Sason M, Godfroy J, et al. Simple model for estimation of radiation absorbed dose by organs and tumors after PRRT from a single SPECT/CT study. EJNMMI Phys. 2021.