Table 5 Univariate and multivariate competing risk regression analyses of Grade 2 or higher radiation necrosis (RN) (n = 156)

Number of BMs

Group A

2.10 (0.67–6.60)

0.200

1.72 (0.53–5.60)

0.370

Group B

Ref

–

Ref

–

Group C

1.21 (0.22–6.52)

0.820

1.13 (0.18–7.15)

0.900

Age (years)

 < 65

Ref

–

Ref

–

 ≥ 65

0.81 (0.28–2.35)

0.700

0.79 (0.24–2.57)

0.690

Gender

Female

Ref

–

Ref

–

Male

1.13 (0.42–2.98)

0.810

0.91 (0.32–2.59)

0.870

Primary site

Lung

Ref

–

Ref

–

GI

0.44 (0.06–3.44)

0.430

0.57 (0.07–4.91)

0.610

Breast

N.A

N.A

N.A

N.A

Others

0.50 (0.11–2.16)

0.350

0.53 (0.11–2.61)

0.440

KPS

 ≥ 80

Ref

–

Ref

–

 ≤ 70

0.48 (0.16–1.48)

0.200

0.52 (0.12–2.21)

0.370

Extracranial lesions

Controlled

Ref

–

Ref

–

Uncontrolled

0.33 (0.12–0.87)

0.025

0.44 (0.15–1.31)

0.140

fSRT or SRS

SRS

Ref

–

Ref

–

fSRT

1.34 (0.51–3.54)

0.560

1.35 (0.35–5.16)

0.670

Total PTV volume (cm³)

1 (≥ 15)

1.10 (0.27–4.59)

0.890

1.57 (0.24–10.33)

0.640

2 (≥ 4, < 15)

1.86 (0.61–5.64)

0.270

2.00 (0.51–

0.320

3 (< 4)

Ref

–

7.91)Ref

–