Stereotactic radiosurgery of brain metastases: a retrospective study

Background: Single-fraction stereotactic radiosurgery (SRS) is an established standard for radiation therapy of brain metastases although recent developments indicate that multi-fractionated stereotactic radiotherapy (FSRT) results in lower radiation necrosis especially for larger metastases, and the same or even better local control in comparison to SRS.

Methods: Seventy-two patients with 111 brain metastases received SRS with a single dose of 18 Gy between September 2014 and December 2021. The dose prescription was either 18 Gy given to the enclosing 80% isodose with a normalization to Dmax = 100% of 22.5 Gy (part I) or 18 Gy = D98, while D0.03 cc of 21.6-22.5 Gy was accepted (part II). The study retrospectively evaluated local progression-free survival (LPFS), response on the first follow-up magnetic resonance imaging (MRI), and radiation necrosis.

Results: Melanoma brain metastases (n = 44) were the most frequent metastases. The median gross tumor volume (GTV) was 0.30 cm³ (IQR, 0.17-0.61). The median follow-up time of all patients was 50.8 months (IQR, 30.4-64.6). Median LPFS was 23.5 months (95%CI 17.2, 29.8). The overall LPFS rates at 12-, 18-, 24- and 30 months were 65.3%, 56.3%, 46.5%, and 38.8%. Brain metastases with radioresistant histology (melanoma, renal cell cancer, and sarcoma) showed a 12-month LPFS of 60.2%, whereas brain metastases with other histology had a 12-month LPFS of 70.1%. The response of brain metastases on first follow-up MRIs performed after a median time of 47 days (IQR, 40-63) was crucial for long-term local control and survival. Eight brain metastases (7.2%) developed radiation necrosis after a median time of 18.4 months (IQR, 9.4-26.5). In multivariate analyses, a GTV > 0.3 cm³ negatively affected LPFS (HR 2.229, 95%CI 1.172, 4.239). Melanoma, renal cell cancers, and sarcoma had a lower chance of LPFS in comparison to other cancer types (HR 2.330, 95%CI 1.155, 4.699).

Conclusions: Our results indicate a reasonable 1-year local control of brain metastases with radiosensitive histology. Radioresistant metastases show a comparatively poor local control. Treatment refinements merit exploration to improve local control of brain metastases.

Trial registration: This study is retrospectively registered (ethics approval number 23-3451-104).