Efficacy of virtual block objects in reducing the lung dose in helical tomotherapy planning for cervical oesophageal cancer: a planning study

Table 4 Dosimetric parameter comparison among a selected series of blockage modes using a semi-circular block

		Non-block (control group)	Block 7 (D)	p	Block 8 (C)	p	Block 8 (D)	p
Lung	V5 (%)	48.0	29.2	< 0.001	26.4	< 0.001	31.3	< 0.001
	V10 (%)	39.4	20.6	< 0.001	20.6	< 0.001	22.4	< 0.001
	V20 (%)	16.0	12.1	0.002	13.3	0.046	13.2	0.028
	VS5 (mL)	1747	2308	0.023	2454	0.004	2299	0.023
	mean dose (Gy)	9.6	6.8	< 0.001	7.0	< 0.001	7.1	< 0.001
Conformity Index		0.85	0.77	0.012	0.79	0.131	0.82	0.616
Homogeneity Index		0.04	0.07	0.001	0.07	0.002	0.05	0.100
Spinal cord PRV max dose (Gy)		47.9	49.7	< 0.001	50.2	< 0.001	49.4	0.002
Body max dose (Gy)		63.3	64.7	0.005	65.2	< 0.001	63.9	0.317
Heart mean dose (Gy)		6.2	7.4	0.564	7.2	0.719	7.0	0.811
Thyroid mean dose (Gy)		53.6	54.0	0.964	55.4	0.315	54.0	0.968
Delivery time (min)		4.9	6.0	< 0.001	6.2	< 0.001	5.6	0.010

V5 lung volume receiving 5 Gy, V10 lung volume receiving 10 Gy, V20 lung volume receiving 20 Gy, VS5 normal pulmonary volume of less than 5 Gy, C complete block mode, D directional block mode, PRV planning risk volume

ISSN: 1748-717X