Table 2 Comparison of baseline characteristics in training, testing and extra validation set

Age (years)

0.577

  ≤ 75

78(57.8)

20(58.8)

9(45.0)

  > 75

57(42.2)

14(41.2)

11(55.0)

Sex

0.873

 Male

96(71.1)

24(70.6)

13(65.0)

 female

39(28.9)

10(29.4)

7(35.0)

BMI (kg/m²)

0.574

  < 18

29(21.5)

7(20.6)

1(5.0)

 18 ≤ X < 24

87(64.4)

22(64.7)

16(80.0)

 24 ≤ X < 28

16(11.9)

4(11.8)

2(10.0)

  ≥ 28

3(2.2)

1(2.9)

1(5.0)

 PS score

(n = 135), %

(n = 34), %

0.686

 0

5(3.7)

2(5.9)

2(10.0)

 1

120(88.9)

30(88.2)

17(85.0)

 2

10(7.4)

2(5.9)

1(5.0)

Lesion location

0.926

 Upper

29(21.5)

8(23.5)

4(20.0)

 Middle

81(60.0)

20(58.8)

14(70.0)

 Distal

25(18.5)

6(17.7)

2(10.0)

Histologic grade

0.928

 Well differentiated

10(7.4)

3(8.8)

1(5.0)

 Moderately differentiated

33(24.4)

9(26.5)

3(15.0)

 Poorly differentiated

17(12.6)

4(11.7)

4(20.0)

 Unknown

75(55.6)

18(53.0)

12(60.0)

T stage

0.445

 T3

53(39.2)

14(41.2)

5(25.0)

 T4

82(60.8)

20(58.8)

15(75.0)

N stage

0.751

 N0

64(47.4)

16(47.1)

11(55.0)

 N1

53(39.3)

13(38.2)

5(25.0)

 N2

18(13.3)

5(14.7)

4(20.0)

Clinical stage

0.837

 stage II

28(20.7)

7(20.6)

3(15.0)

 stage III

59(43.7)

15(44.1)

7(35.0)

 stage IV

48(35.6)

12(35.3)

10(50.0)

Radiation dose (Gy)

0.565

  < 60

85(62.9)

21(61.8)

10(50.0)

  ≥ 60

50(37.1)

13(38.2)

10(50.0)

Treatment regimens

0.128

 CCRT

37(27.4)

10(29.4)

10(50.0)

 RT

98(72.6)

24(70.6)

10(50.0)