Table 1 Characteristics and Predictors of Adjuvant Radiation Therapy (N = 2675)

Age Quartile

Grade^§

N_miss = 158

 Q1 [≤69]

700 (26.2)

 Well differentiated

712 (28.3)

 Q2 [70–75]

701 (26.2)

 Moderately differentiated

1203 (47.8)

 Q3 [76–80]

609 (22.8)

 Poor/Undifferentiated

602 (23.9)

 Q4 [81+]

665 (24.9)

Histology

 Mean (Std) [IQR]

74.8 (8.4) [11]

 Tube/colloid

138 (5.2)

Rural Status

 Other

74 (2.8)

 Metro

1584 (59.2)

 Ductal/lobular

2463 (92.1)

 Urban

967 (36.2)

Lymph Nodes

 Rural

124 (4.6)

 Positive

413 (15.4)

Singh Index

 Negative

2262 (84.6)

 Q1 [Highest SES]

687 (25.7)

ER/PR positive

N_miss = 99

 Q2

674 (25.2)

 Positive

2264 (87.9)

 Q3

649 (24.3)

 Negative

312 (12.1)

 Q4 [Lowest SES]

665 (24.9)

Tumor Size

N_miss = 88

 Mean (Std) [IQR]

86.3 (13.3) [16]

 Q1 [≤ 9 mm]

708 (27.4)

Access to Near Radiation Facilities

 Q2 [10–13]

601 (23.2)

 Q1 [≤2]

1056 (39.5)

 Q3 [14–20]

727 (28.1)

 Q2 [3–4]

497 (18.6)

 Q4 [20+]

551 (21.3)

 Q3 [5]

530 (19.8)

 Mean(Std)[IQR]

15.7 (11.5) [11]

 Q4 [6+]

592 (22.1)

COC status

 Mean (Std) [IQR]

4.7 (4.7) [3]

 Yes

1898 (71.0)

Region

 No

777 (29.1)

 Kentucky

251 (9.4)

SF Number of Beds

N_miss = 32

 North Carolina

504 (18.8)

 Mean (Std) [IQR]

339 (244) [279]

 Ohio

525 (19.6)

SF Radiation Services

N_miss = 45

 Pennsyvlania

1395 (52.2)

 Yes

2031 (77.2)

Marital Status

N_miss = 72

 No

599 (22.8)

 Single

1390 (53.4)

Optional RT

N_miss = 176

 Married

1213 (46.6)

 Yes

1098 (43.9)

Charlson Comorbidity Score

 No

1401 (56.1)

 0

1014 (37.9)

Surg Provider Volume

N_miss = 134

 1

805 (30.1)

 Mean (Std) [IQR]

16.2 (20.3) [20]

 2+

856 (32.0)

Adjuvant Radiation Therapy

 Meand (Std) [IQR]

1.34 (1.62) [2]

 Yes

2128 (79.6)

Medicaid Dual

 No

547 (20.5)

 Yes

387 (14.5)

OS Survival in months^§§

 No

2288 (85.5)

 Observed Mean

5.5 (1.9) [2.0]

Institutionalized

 Yes

163 (6.1)

 No

2512 (94.9))

Stage

 Stage I

1869 (69.9)

 Stage II

697 (26.1)

 Stage III

109 (4.1)

First Cancer

 Yes

2285 (85.4)

 No

390 (14.6)