Local Ablative Strategies After Endovascular Radioembolization

As the median time to radiographic response ranges from 3-8 months in published data, utilization of post-treatment PET/MRI dosimetry offers a powerful mechanism for immediate (within 36 hours) prediction of lesions that are likely to fail radioembolization. This early prediction enables a window for subsequent locoregional therapy prior to re-initiation of systemic chemotherapy. The investigators propose to evaluate patients who are undergoing radioembolization for mCRC using PET/MRI derived dosimetry obtained within 36 hours of the radioembolization procedure. Patients with four tumors or fewer receiving an average dose (Davg) less than 30 Gy will be candidates for subsequent locoregional therapy (stereotactic body radiotherapy (SBRT) or microwave ablation). This strategy will ideally increase the therapeutic index of locoregional therapies, particularly in the patient population who has exhausted their options for systemic therapy. After radioembolization, patients will be divided into 5 strata as per the protocol schema. Patients who receive a Davg greater than 30 Gy in all hepatic lesions will be placed in Stratum 1 and will not undergo subsequent therapy. Patients with four or fewer lesions receiving a Davg less than 30 Gy will be placed in Strata 2, 3, or 4 based on distribution of the underdosed lesions. Stratum 2 will be comprised of patients with four or fewer underdosed lesions less than 3 cm which do not touch vasculature greater than 4 mm in size. Patients in this stratum will receive percutaneous microwave ablation to the underdosed lesions. Stratum 3 will be composed of patients with 4 or fewer underdosed lesions that are not amenable to microwave ablation by virtue of either size (greater than 3 cm) or proximity to hepatic vasculature greater than 4 mm in diameter. These patients will be treated with SBRT to the underdosed lesions. Patients with a combination of lesions some of which are amenable to microwave ablation and some of which are not (due to either size or proximity to vasculature) will be treated in Stratum 4 with a combined approach - microwave ablation to all lesions which are amenable and SBRT to any remaining underdosed lesions. Finally, Stratum 5 will consist of patients with more than 4 underdosed lesions or with disease progression; these patients will be referred for further systemic therapy and are not candidates for further locoregional therapy on study.