Neural stem cell sparing by linac based intensity modulated stereotactic radiotherapy in intracranial tumors

Radiation Oncology

Table 2 Normal brain radiation exposure (median doses [Gy] and 25%- and 75%-quartiles) and conformity index, homogeneity index and quality of coverage of the planning target volume

	Not optimized plan^a	Optimized IMSRT-7	Optimized IMSRT-14	Not optimized vs. IMSRT-7 p	Not optimized vs. IMSRT-14 p	IMSRT 7 vs. IMSRT-14 p
Whole brain exposure
D 10 (Gy) ^b	25.290	26.240	24.450	0.563	0.443	0.783
	Q25: 13.090	Q25:12.280	Q25: 12.400
	Q75: 33.820	Q75: 34.740	Q75: 33.300
D 50 (Gy) ^b	7.000	6.510	6.500	0.589	0.663	0.829
	Q25: 3.960	Q25: 3.550	Q25: 3.480
	Q75: 10.900	Q75: 10.080	Q75: 10.100
D 90 (Gy) ^b	1.400	1.900	1.950	<0.001	<0.001	0.423
	Q25: 1.100	Q25: 1.420	Q25: 1.460
	Q75: 3.280	Q75: 3.300	Q75: 3.280
conformality index ^c	0.980	0.990	1.000	0.003	<0.001	0.005
	Q25: 0.970	Q25: 0.990	Q25: 0.990
	Q75: 1.000	Q75: 1.000	Q75: 1.000
homogeneity index ^c	1.140	1.110	1.090	<0.001	<0.001	<0.001
	Q25: 1.100	Q25: 1.090	Q25: 1.070
	Q75: 1.170	Q75: 1.120	Q75: 1.110
quality of coverage ^c	0.920	0.930	0.920	0.560	0.500	0.757
	Q25: 0.850	Q25: 0.890	Q25: 0.880
	Q75: 0.950	Q75: 0.930	Q75: 0.940

Comparison between not optimized dose distribution and plans optimized for hippocampus and SVZ sparing by intensity modulated stereotactic radiotherapy using 7 or 14 beamlets (IMSRT-7, IMSRT-14). p: p-value from non-parametric Wilcoxon-(rank sum)- test.
^a : 27 plans: 3 D conformal, 20 plans: IMSRT optimized for conventionally contoured organs at risk.
^b : D10, D50, D90: the median dose (Gy) + quartile to 10, 50 and 90% of the normal brain volume (ml) left after the PTV volume was excluded.
^c : conformity index: VRT/TV, homogeneity index: Imax/R, quality of coverage: Imin/RI.

ISSN: 1748-717X