Phase I Dose Escalation Trial of Hypofractionated Radiosurgery for Large Intact or Resected Brain Metastases

Abstract

<h3>Purpose/Objective(s)</h3> Hypofractionated radiosurgery is often used for large brain metastases (BM) not amenable to single fraction radiosurgery, though the ideal dose-fractionation schedule has not been defined. This phase 1 dose escalation study was designed to define the maximum tolerated dose (MTD) of 5 fraction radiosurgery for intact BM or resection cavities ≥ 3cm and < 6cm in maximal dimension. <h3>Materials/Methods</h3> Dose was escalated according to Escalation with Overdose Control (EWOC) method with a planned total enrollment of 24 patients in 8 patient cohorts of 3 patients per cohort and the target highest acceptable dose limiting toxicity (DLT) rate was set at 25%. Enrollment was closed for 4 months in between each cohort. DLT was defined as any acute or late central nervous system CTCAE toxicity grade ≥ 3 considered possibly related to treatment. DLTs assessment extended through 2 years after treatment or was censored at the time of removal from the study or re-irradiation to the treatment site. <h3>Results</h3> Twenty-four patients with 25 target lesions (5 intact BM, 20 resection cavities) were enrolled from October 2012 – February 2021 at the following dose levels with escalation and de-escalation according to EWOC rules: 6 Gy x 5 (level 0, n = 3), 6.5 Gy x 5 (level 1, n = 12), and 7 Gy x 5 (level 2, n = 9). Primary tumor histologies included non-small cell lung cancer (n = 11), esophageal cancer (n = 4), breast cancer (n = 3), melanoma (n = 3), and others (n = 3). The median tumor/cavity size was 18.5cc (range 9.1 - 57.2cc). The median overall follow-up time is 15.6 months (range 0.5 - 81.6) and median DLT assessment follow-up time is 11.5 months (range 0.5 - 27.3). Four DLTs including intracranial hemorrhage (1) and seizure (3) were observe after a median time of 11 months (range 1-14) in 3/9 patients at dose level 2 and 1/12 patients at dose level 1. Two deaths without clear cause in patients with known DLT were considered possibly related to treatment. Symptomatic RN occurred in 4/9 patients at dose level 2, and 2/12 patients at dose level 1. One patient experienced local tumor failure at 36 months. <h3>Conclusion</h3> The 6.5 Gy x 5 fractions is the maximum tolerated dose and recommended phase 2 dose of 5 fraction radiosurgery for large intact or resected brain metastases. This dose level is well tolerated and local control appears promising, though larger studies are required to further assess treatment efficacy at this dose level.