Post SIRT Y-90 time of flight (TOF) PET-MR: Initial experience

Objectives To evaluate post interventional TOF PET-MR in patients undergoing SIRT using Y-90 labeled glass spheres.

Methods Since the beginning of our SIRT activity in early december 2010, we enrolled the first 3 consecutive patients scheduled for SIRT due to hepatocellular carcinoma (HCC) or liver metastases from other tumors into this pilot study. The therapeutic activities were calculated using volumetric CT or MRI and the hepatopulmonary shunt volume as assessed by a pre-therapy Tc-99m-MAA scintigraphy. After intraarterial application of the Y-90 labelled spheres, all patients underwent Brehmsstrahlung-SPECT-CT, followed by hybrid TOF PET-MR on a wole body PET-MR prototype (1 PET bed position centered on the liver followed by a T1 eTHRIVE and a T2 HASTE sequence). Image quality of Y-90 SPECT-CT and PET-MR were assessed using visual scores for lesion detectability and lesion to background contrast compared to pre-interventional exams.

Results The range of injected Y-90 activity was 1.7 to 5 GBq. No immediate or short term side-effects occurred. Post therapeutic SPECT-CT and PET-MR were feasible in all patients with a time consumption of 30 minutes for low dose SPECT-CT and 40 minutes for PET-MR. All previously detected tumor manifestations were visualized by both methods. However, PET-MR showed better lesion discrimination in multifocal disease, higher lesion/background (PET) and better soft tissue (MR) contrasts than SPECT-CT. Additionally, PET-MR provided a quantitative assessment by calculation of standardized uptake values.

Conclusions Y-90-TOF PET-MR proved to be feasible in all patients of this pilot cohort. It was superior to Bremsstrahlung-SPECT-CT in terms of lesion discrimination, lesion/background contrast and quantitative assessment. Given a high frequency of recruitment, more data will be available shortly. PET/MR might be an interesting alternative to post-therapy SPECT-CT, especially in the perspective of future dosimetric studies