2660 - Brain Stereotactic Radiosurgery (SRS) or Fractionated Stereotactic Radiation Therapy (FSRT) with Concurrent or Discontinuated Targeted or Immunotherapy: A Single Center Retrospective Analysis

Purpose/Objective(s): Targeted or immunotherapies have emerged as backbones of systemic treatment in a variety of cancers. In case of limited brain metastases, additional SRS) or FSRT is usually recommended. Because of a lack of data regarding safety of a concurrent use of systemic treatment, no general agreement on the necessity of discontinuation during radiation oncology. Here we report our results with continued or discontinued treatment with regard to efficacy and toxicity.

Materials/Methods: We retrospectively analyzed 92 patients (m:50,f:42), who received either SRS or FSRT to 1-4 brain metastases (127 lesions in total) and had received targeted therapy or immunotherapy prior to RT. Median age was 63 years (24-84). Most patients suffered from melanoma (n=35), followed by NSCLC (n=23), breast cancer (n=9), colorectal cancer (n=7) or renal cancer (n=7). 55 patients (60%) received concomitant (continued) systemic treatment (defined as at least one application within 4 weeks prior or after RT), of whom 30 received at least one application within 7 days from RT. Radiation treatment was planned on fused CT and MRI images within a stereotactic mask and daily IGRT with CBCT. The PTV included the GTV with an isotropic 2 mm.

Results: Median follow-up was 14 months (1-59 months). Dose and fractionation varied based on lesion number, size and location. Main fractionation concepts included 1x 18-22 Gy (60 lesions) for SRS and 5-7x5 Gy (67 lesions) for FSRT. All doses were prescribed to the surrounding 80% isodose. Median GTV size was 1.5 ccm (0.1-102 ccm). 1- and 2y-OS rates for the entire cohort were 68% and 51%. Good performance score (ECOG 0) was significantly associated with improved survival (1y-OS 77%, 2y-OS 64%, p=0.029). Discontinuation of systematic treatment did not result in significantly decreased OS. 1- and 2y-LC rates were 84% and 70% for the entire cohort. Similarly to OS, no significant impact of continuation or discontinuation of systemic treatment was found. 8 patients with in-field recurrences were treated with re-SRS or re-FSRT. Acute and late possibly radiation-related toxicity (any grade) was found in 15% and 7%, respectively. Only 2% each were grade 3. There was no significant difference between the overall acute toxicity rates for patients with concomitant versus discontinued systemic treatment, however the absolute rate of acute toxicities was slightly higher in the concomitant group (16% vs 14%). Of the 8 pts with infield re-SRS or FSRT, 2 developed symptomatic radionecrosis needing surgery, but all are still locally controlled.

Conclusion: Brain SRS or FSRT can be safely applied during systemic treatment with targeted or immunotherapy. Acute low-grade toxicities were slightly but insignificantly increased with concurrent systemic therapy. Concurrent use or discontinuation of systemic treatment did not alter local control or overall survival after brain SRS or FSRT in our cohort. Re-SRS or RE-FSRT were feasible in selected patients with excellent local control and acceptable side effects.