Correlation between dose-volume parameters and rectal bleeding after 12 fractions of carbon ion radiotherapy for prostate cancer

Table 3 The comparison of ratio of rectal bleeding before and after cutoff values of dose-volume parameters calculated by using receiver operating characteristic curves

	Comparison	Number of patients	Ratio of grade 2 rectal bleeding (%)	P value
D 6cc	≥ 34.34 Gy (RBE)	54	5.3	0.42
	< 34.34 Gy (RBE)	202	3.0
D 2cc	≥ 46.46 Gy (RBE)	65	7.7	0.047a
	< 46.46 Gy (RBE)	194	2.1
V 10 Gy (RBE)	≥ 9.85 cc	136	5.9	0.038a
	< 9.85 cc	123	0.8
V 20 Gy (RBE)	≥ 7.00 cc	139	5.8	0.040a
	< 7.00 cc	120	0.8
V 30 Gy (RBE)	≥ 6.91 cc	48	6.0	0.374
	< 6.91 cc	211	6.3
V 40 Gy (RBE)	≥ 4.26 cc	59	1.7	0.689
	< 4.26 cc	200	4.0

^aP < 0.05.

RBE: Relative biological effectiveness.