BackgroundSelective internal radiation therapy with90Y radioembolization aims to selectively irradiate liver tumours by administering radioactive microspheres under the theragnostic assumption that the pre-therapy injection of99mTc labelled macroaggregated albumin (99mTc-MAA) provides an estimation of the90Y microspheres biodistribution, which is not always the case. Due to the growing interest in theragnostic dosimetry for personalized radionuclide therapy, a robust relationship between the delivered and pre-treatment radiation absorbed doses is required. In this work, we aim to investigate the predictive value of absorbed dose metrics calculated from99mTc-MAA (simulation) compared to those obtained from90Y post-therapy SPECT/CT.ResultsA total of 79 patients were analysed. Pre- and post-therapy 3D-voxel dosimetry was calculated on99mTc-MAA and90Y SPECT/CT, respectively, based on Local Deposition Method. Mean absorbed dose, tumour-to-normal ratio, and absorbed dose distribution in terms of dose-volume histogram (DVH) metrics were obtained and compared for each volume of interest (VOI). Mann–Whitney U-test and Pearson’s correlation coefficient were used to assess the correlation between both methods. The effect of the tumoral liver volume on the absorbed dose metrics was also investigated. Strong correlation was found between simulation and therapy mean absorbed doses for all VOIs, although simulation tended to overestimate tumour absorbed doses by 26%. DVH metrics showed good correlation too, but significant differences were found for several metrics, mostly on non-tumoral liver. It was observed that the tumoral liver volume does not significantly affect the differences between simulation and therapy absorbed dose metrics.ConclusionThis study supports the strong correlation between absorbed dose metrics from simulation and therapy dosimetry based on90Y SPECT/CT, highlighting the predictive ability of99mTc-MAA, not only in terms of mean absorbed dose but also of the dose distribution.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13550-023-01011-3.