Survival impact of incidental subventricular zone irradiation in IDH-wildtype glioblastoma

Figures & data

Figure 1. Selection criteria of the IDH-wildtype glioblastoma patient cohort.

Figure 2. Representative illustration of two-dimension segmentation of the ipsilateral (yellow) and contralateral (orange) subventricular zone on radiotherapy planning CT imaging.

Figure 3. The Kaplan–Meier overall survival curves for IDH-wildtype glioblastoma patients according to methylation status of the MGMT gene promoter.

Table 1. Demographical, radiological, molecular and treatment characteristics of 137 IDH-wildtype glioblastoma patients.

Characteristic
Sex, n (%)
Female/male	51 (37.2)/86 (62.8)
Mean age, years (minimum–maximum)	62.2 (31–80)
Preoperative KPS ≥ 70, n (%)	95 (69.3)
Surgery, n (%)
Gross total resection	44 (32.1)
Subtotal resection	58 (42.3)
Biopsy	35 (25.6)
Tumor laterality, n (%)
Left	70 (51.1)
Right	59 (43.1)
Bilateral	8 (5.8)
SVZ contact at diagnosis, n (%)	95 (69.3)
MGMT-promoter, n (%)
Methylated	54 (39.4)
Unmethylated	82 (59.9)
Unknown	1 (0.7)
Survival (months)
Median overall survival (95% CI)	13.3 (12.0–14.7)
Median progression-free survival (95% CI)	6.4 (5.4–7.4)
Planning target volume
Mean volume, mL (SD)	284.7 (108.1)
Median dose, Gy	60.1
Median dose quartiles, Gy (25th,75th)	60.0; 60.5
Ipsilateral SVZ
Mean volume, mL (SD)	19.7 (7.4)
Mean dose, Gy	44.4
Mean dose quartiles, Gy (25th, 50th, 75th)	36.0; 46.9; 53.5
Contralateral SVZ
Mean volume, mL (SD)	25.1 (8.5)
Mean dose, Gy	27.2
Mean dose quartiles, Gy (25th, 50th, 75th)	16.6; 25.6; 36.0

KPS: Karnofsky Performance Score; SVZ: subventricular zone; MGMT: O⁶-methylguanine-DNA-methyltransferase; CI: confidence interval; SD: standard deviation.

Table 2. Univariate survival analysis.

Parameter	Overall survival		Progression-free survival
	HR (95% CI)	p Value	HR (95% CI)	p Value
Age^a	1.005 (0.972–1.039)	.784	0.982 (0.952–1.013)	.241
KPS^b	0.979 (0.964–0.994)	.007	0.980 (0.965–0.994)	.007
STR (vs. biopsy)	0.627 (0.406–0.968)	.035	0.503 (0.320–0.791)	.003
GTR (vs. biopsy)	0.417 (0.261–0.668)	<.001	0.395 (0.240–0.650)	<.001
With SVZ-contact	1.476 (1.011–2.156)	.044	1.773 (1.203–2.611)	.004
MGMTp-methylated	0.362 (0.245–0.534)	<.001	0.432 (0.292–0.640)	<.001
Mean ipsilateral SVZ dose^c	1.014 (0.987–1.043)	.313	1.006 (0.981– 1.031)	.657
Mean contralateral SVZ dose^c	1.029 (1.003–1.057)	.032	1.009 (0.986–1.032)	.448

HR: hazard ratio; CI: confidence interval; KPS: Karnofsky Performance Score; STR: subtotal resection; GTR: gross total resection; SVZ: subventricular zone; MGMTp: O⁶-methylguanine-DNA-methyltransferase gene promoter.

Statistically significant p values in bold.

^a Per increment of one year.

^b Per increment of 10.

^c Per increment of 1 Gy.

Table 3. Multivariate overall survival analysis model for contralateral subventricular zone mean dose.

Parameter	Overall survival
	HR (95% CI)	p Value
Age^a	1.034 (1.014–1.054)	.001
KPS^b	0.986 (0.971–1.001)	.074
Resection (vs. biopsy)	0.432 (0.278–0.669)	<.001
MGMTp-methylated	0.294 (0.196–0.443)	<.001
Contralateral SVZ dose^c	1.016 (0.988–1.046)	.268

HR: hazard ratio; CI: confidence interval; KPS: Karnofsky Performance Score; MGMTp: O⁶-methylguanine-DNA-methyltransferase gene promoter; SVZ: subventricular zone.

Statistically significant p values in bold.

^a Per increment of one year.

^b Per increment of 10.

^c Per increment of 1 Gy.

Data availability statement

Research data are available on request.