Table 3 Predictive factors in-field, marginal or out-field recurrence after fSRT: univariate and multivariate analysis

Age at initial treatment ≥ 60

HR = 0.45 [0.12–1.73]

p = 0.2

HR = 0.74 [0.34–1.64]

p = 0.5

HR = 1.83 [0.84–3.98]

p = 0.13

HR = 3.06 [1.17–8.01],

p = 0.023

Type of initial surgical procedure

- Biopsy

-

-

-

-

-

-

- Subtotal resection

HR = 0.72 [0.17–3.01]

p = 0.7

HR = 1.54 [0.53–4.44]

p = 0.4

HR = 0.58 [0.17–1.98]

p = 0.4

- Gross total resection

HR = 0.24 [0.05–1.22]

p = 0.085

HR = 1.23 [0.46–3.34]

p = 0.7

HR = 1.50 [0.62–3.64]

p = 0.4

Invasion of SVZ at diagnosis

HR = 0.58 [0.07–4.57]

p = 0.6

HR = 0.79 [0.24–2.63]

p = 0.7

HR = 1.95 [0.78–4.83]

p = 0.2

Multifocality of recurrence treated by fSRT

HR = 3.56 [1.00–12.7]

p = 0.050

HR = 3.25 [0.89–11.9]

p = 0.075

HR = 0.93 [0.32–2.70]

p = 0.9

HR = 0.70 [0.24–2.03]

p = 0.5

Adjuvant systemic therapy at recurrence treated by fSRT

HR = 0.54 [0.14–2.09]

p = 0.4

HR = 1.38 [0.63–3.03]

p = 0.4

HR = 1.23 [0.58–2.64]

p = 0.6

KPS score at recurrence treated by fSRT ≥ 70

HR = 0.29 [0.04–2.29]

p = 0.2

HR = 25 655 552 [0 – inf]

p > 0.9

HR = 1.05 [1.00–1.10]

p = 0.051

HR = 0.26 [0.06–1.16]

p = 0.078

HR = 0.97 [0.93–1.00]

p = 0.084

Existence of one or more previous recurrences

HR = 0.70 [0.09–5.49]

p = 0.7

HR = 0.62 [0.15–2.63]

p = 0.5

HR = 2.70 [1.08–6.72]

p = 0.033

HR = 5.29 [1.70–16.5]

p = 0.004

GTV volume

HR = 1.04 [0.99–1.10]

p = 0.13

HR = 1.03 [0.98–1.09]

p = 0.2

HR = 0.97 [0.91–1.003]

p = 0.3

GTV volume ≥ 17 cc

HR = 2.22 [0.47–10.5]

p = 0.3

HR = 2.50 [0.73–8.52]

p = 0.14

HR = 0.68 [0.16–2.89]

p = 0.6

PTV volume

HR = 1.04 [1.00–1.09]

p = 0.055

HR = 1.04 [0.99–1.08]

p = 0.089

HR = 1.02 [0.98–1.06]

p = 0.2

HR = 0.97 [0.93–1.02]

p = 0.2

PTV volume ≥ 36 cc

HR = 2.43 [0.31–19.3]

p = 0.4

HR = 6.23 [1.35–28.7]

p = 0.019

HR = 5.18 [1.06–25.3]

p = 0.042

HR = 0.00 [0.00 – inf]

p > 0.9

GTV-PTV margin 2 and 3 mm vs. 1 mm

HR = 256 164 988 [0 – inf]

p > 0.9

HR = 0.42 [0.18–0.98]

p = 0.044

HR = 0.38 [0.15–0.95]

p = 0.037

HR = 1.85 [0.56–6.18]

p = 0.3