Table 2.
Factors Associated With Hypofractionated vs Conventional Whole Breast Irradiation (WBI) in the Hypofractionation-Permitted Cohort
| No. (%) of Women | Adjusted OR (95% CI)a |
P Value | |||
|---|---|---|---|---|---|
| Conventional, WBI | Hypofractionated, WBI | ||||
| Year, 2008–2013b | 6719 | 1.3 (1.3–1.4) | <.001 | ||
| Patient Factors | |||||
| Age at radiotherapy start | |||||
| ≤49 | 3161 (47.0) | 2767 (87.5) | 394 (12.5) | 0.9 (0.7–1.2) | .50 |
| 50–54 | 923 (13.7) | 817 (88.5) | 106 (11.5) | 1 [Reference] | |
| 55–59 | 1018 (15.2) | 903 (88.7) | 115 (11.3) | 0.9 (0.7–1.3) | .69 |
| 60–64 | 906 (13.5) | 787 (86.9) | 119 (13.1) | 1.1 (0.8–1.5) | .53 |
| 65–69 | 316 (4.7) | 266 (84.2) | 50 (15.8) | 1.3 (0.9–1.9) | .20 |
| 70–74 | 221 (3.3) | 186 (84.2) | 35 (15.8) | 1.3 (0.9–2.0) | .21 |
| ≥75 | 174 (2.6) | 142 (81.6) | 32 (18.4) | 1.4 (0.9–2.3) | .14 |
| Modified Deyo-Charlson Comorbidity Indexc | |||||
| 0 | 4820 (71.7) | 4228 (87.7) | 592 (12.3) | 1 [Reference] | |
| 1 | 1374 (20.4) | 1191 (86.7) | 183 (13.3) | 1.1 (0.9–1.3) | .36 |
| 2 | 337 (5.0) | 298 (88.4) | 39 (11.6) | 0.9 (0.6–1.2) | .43 |
| ≥3 | 188 (2.8) | 151 (80.3) | 37 (19.7) | 1.5 (1.0–2.3) | .03 |
| Radiotherapy technique | |||||
| Non-IMRT | 6187 (92.1) | 5433 (87.8) | 754 (12.2) | 1 [Reference] | |
| IMRT | 532 (7.9) | 435 (81.8) | 97 (18.2) | 1.6 (1.2–2.0) | <.001 |
| Chemotherapy prior to surgery | |||||
| No | 6004 (89.4) | 5223 (87.0) | 781 (13.0) | 1 [Reference] | |
| Yes | 715 (10.6) | 645 (90.2) | 70 (9.8) | 0.6 (0.5–0.8) | .001 |
| Chemotherapy between surgery and WBI | |||||
| No | 2714 (40.4 | 2341 (86.3) | 373 (13.7) | 1 [Reference] | |
| Yes | 4005 (59.6) | 3527 (88.1) | 478 (11.9) | 0.8 (0.7–0.9) | .008 |
| Axillary lymph node involvement | |||||
| No | 5347 (79.6) | 4653 (87.0) | 694 (13.0) | 1 [Reference] | |
| Yes | 1372 (20.4) | 1215 (88.6) | 157 (11.4) | 0.8 (0.6–0.9) | .01 |
| Practice setting | |||||
| Freestanding facility | 2338 (34.8) | 2065 (88.3) | 273 (11.7) | 1 [Reference] | |
| Outpatient hospital | 4381 (65.2) | 3803 (86.8) | 578 (13.2) | 1.1 (1.0–1.3) | .15 |
| Geographic Factors (by Zip Code of Residence) | |||||
| US Census region | |||||
| Northeast | 1543 (23) | 1307 (84.7) | 236 (15.3) | 1 [Reference] | |
| Midwest | 1544 (23) | 1319 (85.4) | 225 (14.6) | 1.0 (0.8,1.2) | .97 |
| South | 1800 (26.8) | 1613 (89.6) | 187 (10.4) | 0.6 (0.5,0.8) | <.001 |
| West | 1772 (26.4) | 1578 (89.1) | 194 (10.9) | 0.6 (0.5,0.8) | <.001 |
| Unknownd | 60 (0.9) | 51 (85.0) | 9 (15.0) | ||
| Population of county of residence | |||||
| ≤250 000 | 1154 (17.2) | 1016 (88.0) | 138 (12.0) | 1 [Reference] | |
| >250 000 | 5498 (81.8) | 4795 (87.2) | 703 (12.8) | 1.0 (0.8–1.2) | .76 |
| Unknownd | 67 (1.0) | 57 (85.1) | 10 (14.9) | ||
| Annual median household income of residents, US $ | |||||
| ≤40 000 | 876 (13) | 784 (89.5) | 92 (10.5) | 1 [Reference] | |
| 40 001–59 999 | 3842 (57.2) | 3355 (87.3) | 487 (12.7) | 1.3 (1.0–1.7) | .07 |
| ≥60 000 | 1890 (28.1) | 1633 (86.4) | 257 (13.6) | 1.5 (1.1–2.1) | .01 |
| Unknownd | 111 (1.7) | 96 (86.5) | 15 (13.5) | 1.2 (0.9–1.6) | |
| Radiation oncologists per 100 000 residentse | 1.1 (1.0–1.2) | .23 | |||
| <High school degree, %f | 1.0 (1.0–1.0) | .09 | |||
Abbreviations: IMRT, intensity-modulated radiotherapy; OR, odds ratio.
Models adjusted for treatment year, age, comorbid disease, history of chemotherapy, axillary lymph node involvement, use of intensity-modulated radiotherapy, density of radiation oncologists, population density of county of residence, percent of resident with less than high school degree, and median household income in the county of residence.
Per 1 year.
Excludes malignancy and ranges from 0 to 25; higher scores indicate greater comorbid disease.
Unknown cases excluded from multivariable analyses.
Per 1 radiation oncologist per 100 000 residents by hospital service area.
Per 1 percentage point.