Purpose:To compare microwave ablation zones created by using sequential or simultaneous power delivery in ex vivo and in vivo liver tissue. Materials and Methods:All procedures were approved by the institutional animal care and use committee. Microwave ablations were performed in both ex vivo and in vivo liver models with a 2.45-GHz system capable of powering up to three antennas simultaneously. Two-and three-antenna arrays were evaluated in each model. Sequential and simultaneous ablations were created by delivering power (50 W ex vivo, 65 W in vivo) for 5 minutes per antenna (10 and 15 minutes total ablation time for sequential ablations, 5 minutes for simultaneous ablations). Thirty-two ablations were performed in ex vivo bovine livers (eight per group) and 28 in the livers of eight swine in vivo (seven per group). Ablation zone size and circularity metrics were determined from ablations excised postmortem. Mixed effects modeling was used to evaluate the influence of power delivery, number of antennas, and tissue type. Results:On average, ablations created by using the simultaneous power delivery technique were larger than those with the sequential technique (P , .05). Simultaneous ablations were also more circular than sequential ablations (P = .0001). Larger and more circular ablations were achieved with three antennas compared with two antennas (P , .05). Ablations were generally smaller in vivo compared with ex vivo. Conclusion:The use of multiple antennas and simultaneous power delivery creates larger, more confluent ablations with greater temperatures than those created with sequential power delivery.q RSNA, 2015

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BACKGROUND Gliomatosis cerebri was removed from the 2016 WHO classification but the clinical problem of gliomatosis remains. For many of these patients, re-irradiation of the whole brain may be the only option. We have employed pulsed reduced dose rate (PRDR) radiation therapy to limit the toxicity of whole brain re-irradiation in this patient population. METHODS Consecutive patients were identified from an institutional database of patients treated with PRDR radiation to the whole brain between 2001 and 2016. Patients were treated by delivering a 20 cGy pulse of radiation every 3 minutes to opposed lateral fields with custom blocks using 6 MV photons, delivering radiation at an effective dose rate of 6.67 cGy/minute. RESULTS A total of sixteen patients were identified who underwent re-treated with WBRT. The median age was 45 (28–66) with a median KPS of 80 (range 60–100). 15 of 16 patients had high grade gliomas. The most common dose was 30 Gy in 15 fractions (range 24–41.4 Gy), giving a median total dose of 90.75 Gy (range 61.4–100.8 Gy). Median overall survival from re-irradiation was 3.8 months (range 0.1–17.0 months) and overall survival from first progression was 11.2 months. 25% of patients survived over 6 months following treatment and the overall response rate was 25% (3 PRs, 1 stable). No grade 4 or grade 5 toxicities were attributable to pulsed reduced dose rate radiation therapy. CONCLUSIONS PRDR radiation therapy provides a potential therapeutic intervention for progressive gliomatosis cerebri, providing a treatment option that can be implemented where no trial is available. As survival is short, these results will assist in counseling patients in considering re-irradiation versus supportive care.