University of Alabama at Birmingham Birmingham, AL
L. Moradi1, R. A. Popple2, R. Travis3, S. Marcrom3, K. Riley4, J. M. Markert4, M. Bredel1, C. D. Willey3, M. C. Dobelbower3, H. Boggs2, R. Sullivan1, and J. B. Fiveash1; 1University of Alabama at Birmingham, Birmingham, AL, 2Department of Radiation Oncology, University of Alabama at Birmingham, Birmingham, AL, 3University of Alabama at Birmingham Department of Radiation Oncology, Birmingham, AL, 4University of Alabama at Birmingham Department of Neurosurgery, Birmingham, AL
Purpose/Objective(s):Single isocenter stereotactic radiosurgery (SRS) is an efficient manner of delivering radiation to patients with multiple brain metastases. At the start of the COVID-19 pandemic, an institutional policy change was implemented which allowed an option for tumors <4cm to be treated with a 3 fraction (fx) regimen rather than a prior 6 Gy x 5 fraction regimen. This study compares local control and toxicities of tumors treated with 3 vs. 5 fx SRS. We hypothesize that the higher Biologically Effective Dose (BED) from 9 Gray (Gy) x 3 fx will result in higher control but may also increase grade 3 or higher toxicity. Materials/
Methods: A retrospective review of 251 patients from 2015 to 2022 was conducted which included 1215 tumors receiving either 9 Gy x 3 fx (27 Gy) or 6 Gy x 5 fx (30 Gy) brain Stereotactic Body Radiation Therapy (SBRT) with all tumors treated with a single isocenter Volumetric Modulated Arc Therapy (VMAT) with manual or automated VMAT (HyperArcTM) treatment planning. Recurrent tumors and post-operative cavities were excluded from the analysis. Local tumor failure was defined as 25% increase in maximum tumor diameter (minimum 3 mm) or more than scant tumor cells at time of salvage surgery. Toxicity included CTCAE V5.0 CNS grade 3 or greater events. Local tumor control and freedom from toxicity were calculated using Kaplan-Meier method and Cox regression models. Results: At 1 year, 358 (29%) tumors that had not failed or had toxicity were evaluable with radiographic and clinical follow-up. Local control for the entire cohort was 92% (±0.010) at one year and 88% (±0.015) at two years. Local control was better with 3 fx regimen compared to 5 fx regimen with 1 year control rate of 97% (± 0.014) vs. 91% (± 0.013) (p = 0.001). When stratifying by tumor equivalent diameter, tumors 2 – 4 cm did not have a statistically significant difference between cohorts whereas tumors <2 cm had significantly improved 1 year local control with 3 fx regimen compared to 5 fx regimen at 97% (±0.017) vs. 91% (±0.014) (p = 0.002). 1 year freedom from grade 3 or higher toxicitywas similar among both groups at 99% (±0.004) and 96% (±0.009) in the 3 fx and 5 fx group, respectively (p = 0.097). Conclusion: 9 Gy x 3 fxfor brain metastases had improved tumor control and comparable toxicity to 6 Gy x 5 particularly among tumors <2cm. 9 Gy x 3 fx may be the preferred regimen when treating multiple tumors with one prescription using single isocenter radiosurgery as it improves efficiency and local control while having similar toxicity.
