PURPOSE: Long axial field-of-view (LAFOV) positron emission tomography/computed tomography (PET/CT) scanners enable high sensitivity and wide anatomical coverage. Therefore, they seem ideal to perform post-selective internal radiation therapy (SIRT) METHODS: In this retrospective analysis, a total number of 32 patients was included (median age 71, IQR 14), which had hepatocellular carcinoma, cholangiocarcinoma, or liver metastases. All patients underwent SIRT, and the post-therapy scan was acquired on a single photon emission computed tomography/computed tomography (SPECT/CT) and a LAFOV Biograph Quadra PET/CT with a 20-minute acquisition time. Post-treatment dosimetry, regarding the tumor, whole-liver and lung (LMD) absorbed dose was done using an organ-wise (Simplicit90Y) and a voxel-wise approach (HERMIA Dosimetry) which used a semi-Monte Carlo algorithm. The lung shunt fraction (LSF) was also measured using the voxel-wise approach and compared to the planned. RESULTS: The planning, post-treatment SPECT and PET (SPECT CONCLUSION: LAFOV PET enabled the direct measurement of post therapy lung dose and tumor doses that correlated well with the planned treatment doses. However, current voxel-wise-based tumor dosimetry seems to be inaccurate for LAFOV PET. In addition, dose volume histogram-based metrics also significantly underestimate the delivered dose. Therefore, improved dosimetry tools are needed for reliable voxel-wise