Table 1.

Radiotherapy dose comparison for the planning target volume (PTV) of primary lesions of nasopharyngeal carcinoma (NPC) and the PGTV (NPC including cervical lymph node metastases) between the flattening filter-free (FFF) beams and flattening filter (FF) beams (cGy, χ²±s).

Planning	PGTV Dmax	PGTV Dmin	PGTV Dmean	PGTV CI	PTV Dmax	PTV Dmin	PTV Dmean	PTV CI
FFF	7831±134	7396±94	6600±329	0.48	7838±133	4180±445	6821±88	0.81
FF	7709±138	7396±94	6566±367	0.45	7716±138	4133±449	6767±62	0.83
t value	−3.06	−3.77	−1.29	2.11	−3.06	−0.44	−3.53	5.42
P value	0.01	0	0.23	0.06	0.01	0.67	0.01	0

FFF – flattening filter-free; FF – flattening filter; PTV – planning target volume; PGTV – PTV for primary lesions of NPC and cervical lymph node metastases; NPC – nasopharyngeal carcinoma; CI – target conformity index; D_max – maximum radiotherapy dose; D_min – minimum radiotherapy dose; D_mean – mean radiotherapy dose.