Table 1 General characteristics of the study patients

Age (years)

Mean

50 ± 15

51 ± 12

.793

48 ± 15

51 ± 12

.372

Sex

Female/Male

37 (64)/21 (36)

17 (52)/16 (49)

.275

18 (55)/15 (46)

17 (52)/16 (49)

1.000

Tumor subsite

Parotid

16 (28)

6 (18)

.394

7 (21)

6 (18)

.692^a

Submandibular

16 (28)

8 (24)

11 (33)

8 (24)

Sublingual

8 (14)

3 (9)

4 (12)

3 (9)

Minor salivary

18 (31)

16 (49)

11 (33)

16 (49)

Performance score

0-1/2

57 (98)/1 (2)

30 (91)/3 (9)

.134^a

33 (100)/0 (0)

30 (91)/3 (9)

.238^a

T stage

T1

23 (40)

5 (15)

.099

12 (36)

5 (15)

.137^a

T2

15 (26)

10 (30)

9 (27)

10 (30)

T3

5 (9)

5 (15)

1 (3)

5 (15)

T4

15 (26)

13 (39)

11 (33)

13 (39)

Tumor size (cm)

Mean

2.4 ± 1.3

3.1 ± 1.7

.051

2.4 ± 1.3

3.1 ± 1.7

.060

N stage

N0

52 (90)

26 (79)

.332^a

31 (94)

26 (79)

.228^a

N1

3 (5)

3 (9)

1 (3)

3 (9)

N2

3 (5)

4 (12)

1 (3)

4 (12)

Disease stage

I

21 (36)

4 (12)

.103

11 (33)

4 (12)

.200^a

II

14 (24)

10 (30)

8 (24)

10 (30)

III

6 (10)

5 (15)

2 (6)

5 (15)

IV

17 (29)

14 (42)

12 (36)

14 (42)

MRI

17 (29)

17 (52)

.044

10 (30)

17 (52)

.132

¹⁸F-FDG-PET

15 (26)

16 (49)

.039

15 (46)

16 (49)

1.000

Surgical margins

<1 mm/≥1 mm

38 (66)/20 (35)

28 (85)/5 (15)

.032

26 (79)/7 (21)

28 (85)/5 (15)

.751

Histological features

Perineural invasion

38 (66)

27 (82)

.147

24 (73)

27 (82)

.558

Nodal ECS

1 (2)

5 (15)

.022^a

0 (0)

5 (15)

.053^a

Bone invasion

9 (16)

11 (33)

.066

8 (24)

11 (33)

.587

Skin invasion

2 (3)

0 (0)

.533^a

1 (3)

0 (0)

1.000^a

Muscle invasion

19 (33)

7 (21)

.335

11 (33)

7 (21)

.408

Lymphatic invasion

5 (9)

4 (12)

.718^a

1 (3)

4 (12)

.355^a

Vascular invasion

2 (3)

3 (9)

.349^a

2 (6)

3 (9)

1.000^a

RT technique

3D-CRT

30 (52)

3 (9)

< .001

8 (24)

3 (9)

.340

IMRT

19 (33)

20 (61)

17 (52)

20 (61)

VMAT

9 (16)

10 (30)

8 (24)

10 (30)

RT dose

>66 Gy

13 (22)

6 (18)

.678^a

5 (15)

6 (18)

.810^a

60–66 Gy

41 (71)

26 (79)

25 (76)

26 (79)

<60 Gy

4 (7)

1 (3)

3 (9)

1 (3)

RT period

2010–2013

13 (22)

12 (36)

.001

11 (33)

12 (36)

.556

2005–2009

15 (26)

17 (52)

11 (33)

17 (52)

2000–2004

30 (52)

4 (12)

11 (33)

4 (12)

Neck treatment

Elective

27 (47)

15 (46)

.677

13 (39)

15 (46)

.411

Therapeutic

8 (14)

7 (21)

4 (12)

7 (21)

None

23 (40)

11 (33)

16 (49)

11 (33)

Treatment time

Surgery to RT (days)

31 ± 12

37 ± 11

.018

35 ± 11

37 ± 11

.544

RT duration (days)

47 ± 9

48 ± 4

.770

46 ± 6

48 ± 4

.189