Kinetics of Circulating Tumor Cells and Survival Outcomes after Stereotactic Radiotherapy/Radiosurgery for Brain Metastases of Breast Cancer

Abstract

starting at 19 Gy and 15 Gy, respectively. Dose increments would begin with 1.5 Gy for metastases between >2 cm to 3 cm and 2.0 Gy for >3 cm to 4 cm. Dose escalation only occurred when a cohort of 3 patients were successfully treated without dose-limiting toxicities after 4 months of treatment. For metastases between >2 cm to 3 cm, 8 patients were treated with a dosage of 19 Gy, 7 patients were treated with a dosage of 20.5 Gy, and 3 patients were treated with a dosage of 22 Gy. For metastases between >3 cm to 4 cm, 5 patients were treated with a dosage of 15 Gy and 2 patients were treated with a dosage of 17 Gy. Patients who underwent this procedure were followed up within a week of treatment, a month of treatment, and subsequently every three months after. Acute toxicities were documented with CTCAE v4.0 grading. Results: Twenty-five patients received SRS treatment at the Cleveland Clinic between 2013 and 2018 on an institutional Phase I/II trial. Eighteen patients with metastasis size >2 cm to 3 cm and seven patients with metastasis size >3 cm to 4 cm were enrolled. Thirteen patients have died at time of analysis. The most common acute side effects from SRS treatment included headache (8 patients), paresthesia (5 patients), weakness (3 patients), and fatigue (3 patients). All acute side effects were Grade I. There did not appear to be increased acute side effects with dose escalation. One patient who received 22 Gy for >2 to 3 cm cohort and one patient who received 17 Gy for the >3 to 4 cm cohort developed radiation necrosis. For the >2 to 3 cm cohort, the highest dose of 22 Gy was reached. For the >3 to 4 cm cohort, the study remains at 17 Gy. Conclusion: SRS treatment of larger brain metastases between >2 cm to 3 cm with 22 Gy resulted in a low risk of acute toxicity and reasonable risk for radiation necrosis. This dose will need to be further studied as a Phase II study to confirm this result and rates of local control.