PET/MRI of Hepatic 90Y Microsphere Deposition Determines Individual Tumor Response

Purpose: The purpose of our study is to determine if there is a relationship between dose deposition measured by PET/MRI and individual lesion response to yttrium-90 (⁹⁰Y) microsphere radioembolization. Materials and Methods: 26 patients undergoing lobar treatment with ⁹⁰Y microspheres underwent PET/MRI within 66 h of treatment and had follow-up imaging available. Adequate visualization of tumor was available in 24 patients, and contours were drawn on simultaneously acquired PET/MRI data. Dose volume histograms (DVHs) were extracted from dose maps, which were generated using a voxelized dose kernel. Similar contours to capture dimensional and volumetric change of tumors were drawn on follow-up imaging. Response was analyzed using both RECIST and volumetric RECIST (vRECIST) criteria. Results: A total of 8 hepatocellular carcinoma (HCC), 4 neuroendocrine tumor (NET), 9 colorectal metastases (CRC) patients, and 3 patients with other metastatic disease met inclusion criteria. Average dose was useful in predicting response between responders and non-responders for all lesion types and for CRC lesions alone using both response criteria (p < 0.05). D70 (minimum dose to 70 % of volume) was also useful in predicting response when using vRECIST. No significant trend was seen in the other tumor types. For CRC lesions, an average dose of 29.8 Gy offered 76.9 % sensitivity and 75.9 % specificity for response. Conclusions: PET/MRI of ⁹⁰Y microsphere distribution showed significantly higher DVH values for responders than non-responders in patients with CRC. DVH analysis of ⁹⁰Y microsphere distribution following treatment may be an important predictor of response and could be used to guide future adaptive therapy trials.