Absorbed dose to lesion and clinical outcome after liver radioembolization with 90Y microspheres. A case report of PET-based dosimetry

A 54-year-old woman with metastatic colorectal carcinoma underwent liver radioembolization with 90Y resin microspheres. Microsphere biodistribution was assessed 2 h after the treatment through a 20-min long 90Y positron emission tomography (PET) scan. Isodose map and lesion dose-volume histogram (DVH) were then evaluated using a MATLAB-based code. Response to therapy was assessed performing a 18F-fluorodexyglucose (FDG) PET 6 months after the treatment. At 90Y PET the patient showed a well-defined horseshoe-shaped hepatic lesion with hot margins and a cold core. The lesion presented a heterogeneous DVH with a hot margin receiving an average radiation dose as high as 287 Gy and a cold area receiving an average radiation dose of 70 Gy approximately. Six months after the treatment the patient reported a complete remission of tumour areas which received a high radiation dose, while progression of metastases was observed in the area that presented scarce microsphere localization at 90Y PET. According to our experience, the use of 90Y PET voxel dosimetry may provide a useful tool to assess possible correlations between microsphere biodistribution and clinical outcome of the treatment. In agreement with current literature findings, an average radiation dose greater than approximately 100 Gy may be required to sterilize liver metastases. (author)