Dose-response evaluation after Yttrium-90 resin microsphere radio-embolization of breast cancer liver metastases

Full text of publication follows. Aim: Yttrium-90 resin microsphere radio-embolization is a valuable therapeutic option in metastatic breast cancer patients with progressive disease refractory to chemotherapy. The goal of this study was to evaluate the dose-response relationship of liver metastasis based on a 3D voxelized ⁹⁰Y PET dosimetry. Materials and methods: we studied the dose-response relationship of twelve hepatic lesions in four selected patients with metastatic breast cancer who underwent ⁹⁰Y radio-embolization (Sirtex SIR-Spheres Pty Ltd.). The administered activity ranged from 1 to 1.3 GBq. Ten days before treatment, patients underwent a baseline ¹⁸F-FDG PET/CT. The determination of the ⁹⁰Y-microsphere activity to administer for treatment was based on the BSA method refined with the partition model derived from a ^99mTc-MAA SPECT/CT performed a week prior to radio-embolization. Within 24 hours after treatment, ⁹⁰Y TOF PET/CT imaging was performed. A follow-up ¹⁸F-FDG PET/CT was performed 1 month after the treatment to evaluate the response to radio-embolization. For each patient, 3D voxelized dose-maps were obtained from the post-treatment ⁹⁰Y TOF PET/CT. A volume of interest (VOI) was drawn for each selected hepatic lesion using the baseline ¹⁸F-FDG PET/CT. To obtain dose-volume histogram (DVH) for each lesion, image co-registration and VOI masks were generated using the PMOD 3.4 software and then exported in Matlab for dose calculation. Furthermore, the average absorbed dose in lesions was corrected for PVE effects by multiplication for appropriate (phantom-based) recovery coefficients according to the lesion size. Early metabolic lesion response was assessed in terms of variation in the maximum standard uptake value (ΔSUVmax) between baseline and follow-up ¹⁸F-FDG PET/CT. The average absorbed dose for each lesion was associated with the respective metabolic response. Results: for the 12 selected lesions, the average volume was 35 cm³ (range 8-147 cm³) and the average absorbed dose was 92 Gy (range 32-137 Gy). We observed a reduced average absorbed dose as the volume of the lesion increased. Metabolic response was observed for all lesions with a measured average ΔSUVmax of -66% (range -28% to -83%). The observed dose-response relationship suggests that better metabolic response was obtained in lesions receiving the higher dose. Conclusions: three-dimensional voxelized dose-map based on ⁹⁰Y TOF PET/CT imaging is an effective tool for assessing tumor dose-response relationship. Patients with breast cancer liver metastases showed good short-term metabolic responses with average absorbed doses to lesions ranging between 32 and 137 Gy. A trend showing improved metabolic response in lesions receiving higher doses was observed. (authors)