PT - JOURNAL ARTICLE AU - Tranel, Jonathan AU - Feng, Felix AU - Hope, Thomas AU - St. James, Sara TI - Impact of cellularity and heterogeneity on deposited absorbed dose patterns of alpha and beta emitters in a model of tumoral clusters. DP - 2021 May 01 TA - Journal of Nuclear Medicine PG - 1564--1564 VI - 62 IP - supplement 1 4099 - http://jnm.snmjournals.org/content/62/supplement_1/1564.short 4100 - http://jnm.snmjournals.org/content/62/supplement_1/1564.full SO - J Nucl Med2021 May 01; 62 AB - 1564Objectives: In the context of targeted radionuclide therapy (TRT), increasing the radiation dose to tumors while minimizing dose to organs at risk may be possible with alpha emitters (<100 μm range). Although is of concern when TRT requires a specificity below the millimeter that beta emitters are unable to provide. In order to attain the absorbed dose (AD) to tumors, the radionuclides physical properties should be considered such as the nature of the particles (alpha, beta), kinetic energy and physical half-lives. This work aims to elucidate AD patterns among alpha (225Ac) and beta (177Lu) emitters in TRT according to the degree of tumor cellularity and uptake. Methods: AD calculations were performed through Convolution/Superposition algorithm using Python 3.7.7 in a 53 mm3 (2503) voxels of tumor cubic model using 20x20x20 μm3 sampling. Each voxel corresponds approximately to a cell, using liver density (1.06 g.cm-3) and composition (ICRP 110). First, tumor cells were organized as clusters with two cellularities: low (25%) and high (75%). Second, each cluster is associated with an uptake intensity value. Two distributions of the uptake values were implemented: a homogenous where all uptake equals 0.5 and a heterogeneous where uptakes are distributed equally between 0 and 1 (). Hence, absorbed dose calculations were performed for a total of four distributions. The whole energy emissions spectra, daughters and relative biological effectiveness (RBE) were considered for the radionuclides with no biological clearance (cumulative activity). Results: Results in Bd per kBq (Bd is Gy equivalent with the RBE considered) were analyzed with 3D transverse slices showing AD gradients and Dose Volume histograms. The delivered absorbed doses are correlated to the physical properties of the radioemitters. For the heterogeneous distribution and the lowest cellularity (25%), the alpha-emitter 225Ac had the most variable AD since the maps show distinct patterns and DVHs have the smoothest shapes. Conversely, 177Lu own the most homogenous AD distribution for the homogeneous distribution and the highest cellularity (75%) as the associated maps are the blurriest and the DVH slope the sharpest. Conclusions: These findings show that the choice of the radionuclide is crucial since this study depicts complex AD pattern according to the tumor cellularity and uptake values. Extension of this study to various sizes and more complex patterns may help to a comprehensive understanding, leading to a personalized dosimetry in the context of TRTs.