Stereotactic radiosurgery for resected brain metastases: Does the surgical corridor need to be treated?

2068 Background: Post-operative stereotactic radiosurgery (SRS) is the standard of care for resected brain metastases, but SRS techniques are not standardized. Although expert consensus guidelines recommend that the surgical corridor leading to the resection cavity be included in the SRS plan, this statement is not based on data. We analyzed the patterns of failure and toxicity with post-resection SRS, with the hypothesis that the corridor needs not be targeted with SRS. Methods: In this IRB-approved retrospective review, from 428 lesions treated from 2005-2018 with post-resection SRS, 58 lesions (57 patients) had evaluable data and a ‘deep’ tumor with a surgical corridor defined as ≥ 1.0 cm from the surface pre-operatively. SRS targeted the surgical corridor, defined as the surgical tract uninvolved by tumor on pre-operative imaging, in 33(57%). Brain failure was defined as local (LF) if within the surgical cavity involved with tumor pre-resection, corridor (CF) if within the surgical tract leading to the surgical cavity, distant (DF) if a new parenchymal tumor, or leptomeningeal (LMD) for new nodular/classical leptomeningeal enhancement. The cumulative incidences of failure and adverse radiation effect (ARE) were analyzed with death and whole brain radiation therapy as competing risks. Results: The median follow-up was 14 months. Not targeting surgical corridor was associated with prior SRS/resection for other brain metastases (23% vs. 0%, p=0.01), deeper tumors (median 2.1 cm vs. 1.4 cm, p<0.01), and systemic treatment within 3 months (p =0.01), but not other factors (p>0.10). The 12-month failure rates, if surgical corridor was not treated vs. treated, respectively, were: CF 8% (1-24%) vs. 0% (p=0.12), LF 4% (0-17%) vs. 13% (4-27%) (p=0.32), LMD 40% (19-61%) vs. 10% (2-23%) (p=0.03), DF 65% (43-81%) vs. 35% (19-52%) (p=0.02), and ARE 8% (1-22%) vs. 13% (4-28%) (p=0.35). After adjusting for systemic treatment, differences were not statistically significant (p>0.05). Conclusions: Omitting the surgical corridor in post-operative SRS for resected brain metastases was not associated with statistically significant differences in recurrences or adverse radiation effect. Surgical corridor does not need to be included in all post-resection SRS.