Pretreatment Dosimetry in HCC Radioembolization with 90Y Glass Microspheres Cannot Be Invalidated with a Bare Visual Evaluation of 99mTc-MAA Uptake of Colorectal Metastases Treated with

Ulrich et al. (1) reporting on the predictive value of 99mTc-macroaggregated albumin (99mTc-MAA) uptake in patients with colorectal liver metastasis scheduled for selective internal radiation therapy (SIRT) with 90Y-loaded resin microspheres. Despite the inclusion of an impressive amount of work (66 patients and 435 lesions), the results are disappointing as they found no association between patient- or lesion-based response and the overall degree of 99mTc-MAA perfusion (P 5 0.172). The authors conclude that the response cannot be predicted by the degree of perfusion on 99mTc-MAA scintigraphy. This study raises several important methodologic and general concerns that have to be clarified. In our opinion, conclusions made by the authors cannot be supported by data presented in this paper. From a methodologic point of view, we have 4 major concerns: the insufficient quantification method, lack of dosimetric evalua