Table 1.
Factors Associated With Hypofractionated vs Conventional Whole Breast Irradiation (WBI) in the Hypofractionation-Endorsed Cohort
| No. (%) of Women | Adjusted OR (95% CI)a |
P Value | |||
|---|---|---|---|---|---|
| Total | Conventional WBI | Hypofractionated WBI | |||
| Year, 2008–2013b | 8924 | 1.4 (1.3–1.4) | <.001 | ||
| Patient Factors | |||||
| Age at radiotherapy start, y | |||||
| 50–54 | 1745 (19.6) | 1477 (84.6) | 268 (15.4) | 1 [Reference] | |
| 55–59 | 1933 (21.7) | 1596 (82.6) | 337 (17.4) | 1.1 (0.9–1.4) | .17 |
| 60–64 | 2201 (24.7) | 1777 (80.7) | 424 (19.3) | 1.3 (1.1–1.6) | .003 |
| 65–69 | 1121 (12.6) | 867 (77.3) | 254 (22.7) | 1.6 (1.3–1.9) | <.001 |
| 70–74 | 803 (9.0) | 614 (76.5) | 189 (23.5) | 1.7 (1.4–2.2) | <.001 |
| ≥75 | 1121 (12.6) | 791 (70.6) | 330 (29.4) | 2.5 (2.0–3.0) | <.001 |
| Modified Deyo-Charlson Comorbidity Indexc | |||||
| 0 | 5647 (63.3) | 4536 (80.3) | 1111 (19.7) | 1 [Reference] | |
| 1 | 2141 (24.0) | 1704 (79.6) | 437 (20.4) | 0.9 (0.8–1.1) | .30 |
| 2 | 713 (8.0) | 571 (80.1) | 142 (19.9) | 0.8 (0.7–1.0) | .05 |
| ≥3 | 423 (4.7) | 311 (73.5) | 112 (26.5) | 1.1 (0.8–1.3) | .68 |
| Radiotherapy technique | |||||
| Non-IMRT | 8096 (90.7) | 6518 (80.5) | 1578 (19.5) | 1 [Reference] | |
| IMRT | 828 (9.3) | 604 (72.9) | 224 (27.1) | 1.5 (1.3–1.8) | <.001 |
| Practice setting | |||||
| Freestanding facility | 3029 (33.9) | 2499 (82.5) | 530 (17.5) | 1 [Reference] | |
| Outpatient hospital | 5895 (66.1) | 4623 (78.4) | 1272 (21.6) | 1.4 (1.3–1.6) | <.001 |
| Geographic Factors (by Zip Code of Residence) | |||||
| US Census region | |||||
| Northeast | 2289 (25.6) | 1782 (77.9) | 507 (22.1) | 1 [Reference] | |
| Midwest | 1906 (21.4) | 1526 (80.1) | 380 (19.9) | 0.9 (0.8–1.1) | .35 |
| South | 2039 (22.8) | 1651 (81.0) | 388 (19.0) | 1.0 (0.9–1.2) | .93 |
| West | 2592 (29) | 2077 (80.1) | 515 (19.9) | 1.0 (0.9–1.2) | .81 |
| Unknownd | 98 (1.1) | 86 (87.8) | 12 (12.2) | ||
| Population of county of residence | |||||
| ≤250 000 | 1450 (16.2) | 1174 (81.0) | 276 (19.0) | 1 [Reference] | |
| >250 000 | 7366 (82.5) | 5855 (79.5) | 1511 (20.5) | 0.9 (0.8–1.1) | .41 |
| Unknownd | 108 (1.2) | 93 (86.1) | 15 (13.9) | ||
| Median household income of residents, US $ | |||||
| ≤40 000 | 1206 (13.5) | 1002 (83.1) | 204 (16.9) | 1 [Reference] | |
| 40 001–59 999 | 5232 (58.6) | 4187 (80.0) | 1045 (20.0) | 1.1 (0.9–1.4) | .24 |
| ≥60 000 | 2309 (25.9) | 1781 (77.1) | 528 (22.9) | 1.3 (1.0–1.6) | .05 |
| Unknownd | 177 (2.0) | 152 (85.9) | 25 (14.1) | ||
| Radiation oncologists per 100 000 residentse | 1.1 (1.1–1.2) | .001 | |||
| <High school degree, %f | 1.0 (1.0–1.0) | .001 | |||
Abbreviations: IMRT, intensity-modulated radiotherapy; OR, odds ratio.
Models are adjusted for treatment year, age, comorbid disease, use of intensity-modulated radiotherapy, density of radiation oncologists, population density of county of residence, percent of resident with less than a high school degree, and median household income in the county of residence.
Per 1 year.
The modified Deyo-Charlson Comorbidity Index excludes malignancy and ranges from 0 to 25 with higher scores indicating 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.