Hypofractionated Stereotactic Radiation Therapy to the Surgical Bed for Patients With Brain Metastases Provides Effective Local Control for Bed ≥ 48

Abstract

HSRT directed for large surgical beds in patients with resected brain metastases improves local control while sparing patients the toxicity associated with whole brain radiation. We review our institutional series to determine factors predictive of local failure. In a total of 38 consecutive patients with brain metastases treated from August 2011-August 2016, 40 surgical beds were treated with HSRT in 3 or 5 fractions. Each surgical bed was treated as a unique data point. All treatments were completed on a robotic radiosurgery platform using the 6D Skull tracking system. Volumetric MRIs from before and after surgery were used for radiation planning. A 2 mm PTV margin was used around the contoured surgical bed +/- resection margins and these were reviewed by the radiation oncologist and neurosurgeon. Lower total doses were prescribed based on proximity to critical structures or if prior radiation treatments were given. Local control in this study is defined as no volumetric MRI evidence of recurrence of tumor within the high dose radiation volume. Statistics were calculated using JMP Pro v12.1. Of the 40 surgical beds analyzed, 23 were from NSCLC, 5 were from breast, 4 from melanoma, 2 from esophagus, and 1 each from SCLC, sarcoma, colon, renal, rectal, and unknown primary. 9 were treated with 3 fractions with median dose 24Gy and 31 were treated with 5 fractions with median dose 27.5Gy using an every other day fractionation. There were no reported grade 3 or higher toxicities. Median follow up was 212 days after completion of radiation. 10 (33%) surgical beds developed local failure with a median time to failure of 148 days. All but 3 patients developed new brain metastases outside of the treated field and were treated with stereotactic radiosurgery, whole brain radiation and/or chemotherapy. 5 patients (13%) developed leptomeningeal disease. With a median follow up of 226 days, 30 Gy/5 fx was associated with the best local control (93%) with only 1 local failure. A lower total dose in 5 fractions (ie 27.5 Gy or 25 Gy) had a local control rate of 70%. For 3 fraction SBRT, local control was 100% using a dose of 27 Gy in 3 fractions (follow up was >600d) and 70% if 24 Gy in 3 fractions was used. A higher total BED (α/β=10) was statistically significant for improved local control (p=0.04) with a threshold BED of 48 or higher associated with better local control. HSRT after surgical resection for brain metastasis is well tolerated and has improved local control with BED>=48 (30Gy/5fx and 27Gy/3fx). Additional study is warranted.