Dosimetric Comparisons of Volumetric Modulated Arc Therapy and Tomotherapy for Early T-Stage Nasopharyngeal Carcinoma

Table 2

Dosimetric comparisons of PTVs between RapidArc and HT plans.

		RapidArc	HT	P-value
		Average (SD)	Average (SD)
D98(cGy)	PGTVnx	6930 (91)	6938 (88)	NS
	PGTVnd	6978 (83)	6964 (102)	NS
	PTV1	6066 (154)	6098 (146)	NS
	PTV2	5331 (258)	5391 (144)	NS
HI	PGTVnx	0.073 (0.013)	0.073 (0.013)	NS
	PGTVnd	0.076 (0.011)	0.07 (0.011)	NS
	PTV1	0.201 (0.034)	0.205 (0.026)	NS
	PTV2	0.31 (0.071)	0.297 (0.073)	NS
CI	PGTVnx+nd	0.818 (0.025)	0.861 (0.033)	0.004
	PTV1	0.453 (0.246)	0.515 (0.268)	NS
	PTV2	0.627 (0.269)	0.591 (0.245)	NS

SD: standard deviation; D98: the maximum dose encompassing 98% of PTV; HI: homogeneity index; CI: conformity index. The CI of PGTVnx and PGTVnd were calculated integrally because they were given the same prescription dose.