Y-90 microspheres treatment response monitoring: PET/CT or diagnostic MR ?

Objectives The intra-arterial administration of Y-90 microspheres is a new palliative treatment for unresectable liver malignancies. However, there is no widely accepted imaging protocol for treatment response monitoring. Our aim was to compare the accuracy of FDG-PET/CT and a standard-protocol liver MR in evaluating response to Y-90 microspheres embolisation.

Methods We evaluated 25 patients who underwent Y-90 microspheres embolisation (SIR-Spheres, Sirtex Medical Ltd., Sydney, Australia) for pathologically proven liver malignancy. Baseline imaging studies prior to treatment as well as post-treatment CT, MR, or PET/CT scans were reviewed. A subset of 4 patients had post-treatment MR and PET/CT scans not more than 1 mo apart. Both studies were examined in comparison to each other and against the results of long-term clinical or imaging follow-up to determine if PET/CT is more accurate than MR in defining treatment response and directing patient management.

Results 25 patients were treated with SIR-Spheres in our institution in the above time interval. 4 patients were treated for primary liver malignancy; the others had metastatic liver disease. All patients had diagnostic liver MR 4 to 8 weeks after the treatment. 4 patients also had FDG-PET/CT scan performed not more than 4 weeks apart from the MR. In 3 out of 4 patients, the MRI demonstrated grossly stable appearance of the liver when compared to pre-treatment imaging suggestive of stable liver disease, whereas PET/CT showed no hypermetabolic activity in the treated lesions consistent with no residual disease. None of these patients had liver disease recurrence in the next 22 months. In 1 patient, both modalities showed metastatic disease progression, which was confirmed by CT follow up 3 months later.

Conclusions FDG-PET/CT imaging may be a more accurate assessment of therapy response following Y-90 microspheres embolisation than liver MR; larger cohort of patients is currently under evaluation.