Dosimetric benefit to organs at risk following margin reductions in nasopharyngeal carcinoma treated with intensity-modulated radiation therapy

Table 5 Dosimetric comparison of plans with pre-correction margins and plans with post-correction margins for the PTVs in 40 NPC patients

Target	Dose index	Plan with pre-correction margins	Plan with post-correction margins	Difference	P value
PTV_7000	D_2% (Gy)	76.2 ± 0.84	75.97 ± 0.79	0.28 ± 0.57	0.003
	D_50% (Gy)	73.79 ± 0.43	73.59 ± 0.38	0.19 ± 0.32	<0.001
	D_95% (Gy)	71.05 ± 0.32	71.06 ± 0.26	−0.01 ± 0.16	0.738
	D_98% (Gy)	69.53 ± 1.34	69.80 ± 1.01	−0.27 ± 0.44	<0.001
	HI	0.09 ± 0.03	0.08 ± 0.02	0.01 ± 0.01	<0.001
PTV_6000	D_2% (Gy)	75.77 ± 0.85	75.44 ± 0.80	0.33 ± 0.48	<0.001
	D_50% (Gy)	71.18 ± 1.29	70.79 ± 1.22	0.39 ± 0.30	<0.001
	D_95% (Gy)	64.00 ± 1.06	63.85 ± 1.06	0.16 ± 0.44	0.030
	D_98% (Gy)	62.33 ± 1.04	62.34 ± 1.07	−0.02 ± 0.45	0.805
	HI	0.19 ± 0.02	0.18 ± 0.02	0.01 ± 0.01	0.010
PTV_5600	D_2% (Gy)	74.60 ± 1.04	74.33 ± 1.06	0.27 ± 0.38	<0.001
	D_50% (Gy)	62.58 ± 0.77	62.41 ± 0.83	0.17 ± 0.40	0.009
	D_95% (Gy)	57.81 ± 0.56	57.72 ± 0.54	0.09 ± 0.22	0.018
	D_98% (Gy)	55.69 ± 1.06	55.70 ± 1.08	−0.01 ± 0.35	0.990
	HI	0.30 ± 0.03	0.29 ± 0.03	0.01 ± 0.01	0.002

All data are presented as mean ± SD of 40 patients. HI, homogeneity index; D_2%, dose received by 2% of the volume; D_50%, dose received by 50% of the volume; D_95%, dose received by 95% of the volume; D_98%, dose received by 98% of the volume. Other abbreviations as in Tables 3 and 4.

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