90Y-PET for the assessment of microsphere biodistribution after selective internal radiotherapy

Objectives To demonstrate the feasibility of Y-90-PET imaging for biodistribution assessment after selective internal radiotherapy treatments with Y-90-microspheres, comparing the results with Tc-99m-macroaggregated albumin (MAA) images obtained with single-photon emission computed tomography. Methods Preliminary studies were performed with the aim of evaluating the imaging system spatial resolution and scanner sensitivity for detecting annihilation photons. Subsequently, microsphere distribution was evaluated in 10 patients who underwent liver selective internal radiotherapy treatment. Tc-99m-MAA and Y-90-microsphere were simultaneously injected for immediate monitoring after treatment. For each patient, the metastases detected with Y-90-PET and Tc-99m-MAA were assessed and compared with F-18-fluorodeoxyglucose-PET (F-18-FDG-PET) obtained before treatment and used as an imaging benchmark procedure. The correlation between these techniques was thus investigated in terms of matching lesions. Lesions were considered true positive in the case of matching with F-18-FDG-PET. The sensitivity of both techniques was evaluated as the true-positive fraction of detected spots in the treated liver sectors. Results With our experimental setup, a maximum scanner sensitivity of .577 and 0.077 cps/MBq was obtained for three-dimensional and two-dimensional acquisitions, respectively. A good correlation was obtained between images obtained before and after treatment, with Y-90-PET being by far the most accurate technique in detecting microsphere distribution and tumor nonhomogeneity areas. A sensitivity as high as 0.91 was obtained with Y-90-PET, whereas Tc-99m-MAA imaging showed a SE of 0.75. Conclusion Y-90-PET is a promising and reliable technique for microsphere biodistribution evaluation after liver selective internal radiotherapy treatment. Because of the better resolution and the possibility to perform computed tomography fusion, Y-90-PET images are more accurate than Tc-99m-MAA single-photon emission computed tomography, which is now considered the gold standard for biodistribution assessment. Nucl Med Commun 33:198-204 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.