A prospective trial of volumetric intensity-modulated arc therapy vs conventional intensity modulated radiation therapy in advanced head and neck cancer

Table 1 Critical structure dose tolerances

Critical structure/organ at risk	Dose (Gy)
Ant tongue (1/2 or 1/3)	70
Brainstem	54
Brain - 50%	54
Brachial plexus	60
Spinal cord	45
Cochlea	30
Parotid – 50%	30

Table 2 Patient characteristics

Pt	Pathology/site/stage			HD	ID	ED	Plan
1	SCC	Oropharynx	T3N3	70		56	VMAT
2	SCC	Larynx	T4N0	70	63	56	VMAT
3	SCC	Oropharynx	T2N2A	70		60	VMAT
4	SCC	Larynx	T3N2B	66		66	VMAT
5	SCC	Larynx	T3N2C	70		56	VMAT
6	SCC	Oropharynx	T2N2B	70		56	VMAT
7	SCC	Oropharynx	T3N0	70		56	VMAT
8	SCC	Larynx	T4N2C	70		56	VMAT
9	SCC	Nasopharynx	T1N3	70	60	55	VMAT
10	SCC	Oropharynx	T1N1	66		56	VMAT
11	SCC	Larynx	T3N0	70		56	VMAT
12	Medullary	Thyroid	T4bN1b	66		66	VMAT
13	SCC	Oropharynx	T4N2C	70		63	VMAT
14	SCC	Oropharynx	T2N2C	70		56	VMAT
15	SCC	Hypopharynx	T2N3	70		56	VMAT
16	SCC	Oropharynx	T2N3	70		60	VMAT
17	SCC	Larynx	T3N0	70		56	IMRT
18	SCC	Oropharynx	T3N2C	70		56	IMRT
19	SCC	Oropharynx	T3N2B	70		56	VMAT
20	SCC	Oropharynx	T2N1	70		56	VMAT

SCC: Squamous cell carcinoma; HD: High dose; ID: Intermediate dose; ED: Elective dose. VMAT: Volumetric modulated arc therapy; IMRT: Intensity modulated radiation therapy.

Table 3 Target volume dose delivery analysis of volumetric intensity-modulated arc therapy (two arcs) and intensity modulated radiation therapy (seven to ten sliding window fields) plans

	Monitor units		Conformity index		Dose Homogeneity
Patient	VMAT	IMRT	VMAT	IMRT	VMAT	IMRT
1	431	2211	1.15	1.19	2.47	2.59
2	530	1264	2.69	1.85	1.23	1.78
3	465	1853	1.74	1.97	1.31	2.34
4	584	1681	1.34	1.35	1.61	2.33
5	526	1423	1.69	1.38	1.15	1.95
6	593	1560	2.00	1.43	1.07	2.01
7	552	2046	1.79	1.66	1.08	2.34
8	522	1579	1.34	1.28	2.06	2.66
9	672	1473	1.72	1.70	0.98	2.46
10	668	1359	1.90	1.42	2.38	1.91
11	614	1000	3.07	1.67	1.05	0.79
12	533	2047	1.27	1.38	1.92	1.42
13	483	2087	1.86	1.58	1.41	2.05
14	531	1319	1.65	1.23	1.27	2.06
15	544	1188	2.41	1.67	1.58	1.27
16	520	1769	2.50	2.43	1.69	1.06
17	519	1114	3.27	2.39	1.11	1.19
18	542	1273	1.63	1.64	1.31	0.81
19	565	1258	2.16	1.84	1.44	1.01
20	463	1135	3.95	2.26	0.98	0.58
Mean	542.85	1612.58	2.00	1.61	1.45	1.73
P value	< 0.001		0.003		0.069

Comparison of monitor units required, conformity using conformity index and dose homogeneity using standard deviation of dose to PTV_HD. A lower CI corresponds to the more conformal plan. A lower standard deviation is seen in a more homogeneous plan. VMAT: Volumetric intensity-modulated arc therapy; IMRT: Intensity-modulated radiation therapy.

Table 4 Mean dose to organs at risk across all intensity modulated radiation therapy and volumetric intensity-modulated arc therapy plans

	Mean dose (Gy)		P value
	IMRT	VMAT
Ant tongue	52.7	51.1	0.135
Brainstem	15.3	14.3	0.264
Left cochlea	23.7	18.8	0.002
Right cochlea	22.4	19.3	< 0.001
Left parotid	46.8	46.5	0.68
Right parotid	47.3	46.7	0.373
Spinal cord	20.4	20.9	0.173

VMAT: Volumetric intensity-modulated arc therapy; IMRT: Intensity-modulated radiation therapy.