Reduced-dose WBRT combined with SRS for 1-4 brain metastases aiming at minimizing neurocognitive function deterioration without compromising brain tumor control.

Background and purpose: To minimize cognitive decline without increasing brain tumor recurrence (BTR) by reduced-dose whole-brain radiotherapy (RD-WBRT) (25 Gy, 10 fractions) + stereotactic radiosurgery (SRS) in patients with ≤ 4 brain metastases. Materials and methods: Eligible patients with ≤ 4 brain metastases on contrast-enhanced MRI and Karnofsky Performance Status ≥ 70. The primary endpoint was the non-inferiority of BTR at distant sites in the brain (BTR-distant)-free survival at 6 months compared to that of the standard dose (SD)-WBRT (30 Gy, 10 fractions) + SRS arm in a randomized clinical trial (JROSG99-1) of SRS with/without SD-WBRT. Secondary endpoints included BTR at any brain sites (BTR-all) and neurocognitive function assessed by a six-test standardized battery. Results: Forty patients from seven institutions were enrolled (median age 69 years). The primary tumor site was a lung in 28 patients; 20 patients had a solitary brain metastasis. The median survival time was 19.0 months (95 %CI: 13.8 %-27.5 %). The BTR-distant-free survival at 6 months was 76.9 % (59.5 %-87.7 %), which is comparable to that of historical control although predetermined non-inferiority (>71 %) could not be confirmed (p = 0.16). The cumulative incidence of BTR-all at 6 months accounting for the competing risk of death was 23.0 % (11.4-37.1), which was not worse than that of historical control (p = 0.774). The frequency of the cumulative incidence of persistent cognitive decline at 6 months was 48.6 % under the [>2.0 SD in ≥ 1 test] definition. Conclusions: RD-WBRT may yield comparable intracranial tumor control when combined with SRS, and may reduce the risk of neurocognitive decline compared to that after SD-WBRT.