Table 3. Multivariable analysis for survival (with and without propensity matching).
| Characteristic | HR for survival | 95% CI | P |
|---|---|---|---|
| Non-propensity matched | |||
| Type of radiotherapy | |||
| SBRT | 1 | Reference | |
| PBT | 0.70 | 0.43–1.04 | 0.07 |
| Race | |||
| White | 1 | Reference | |
| Black | 0.88 | 0.65–1.20 | 0.43 |
| Other | 0.57 | 0.38–0.86 | 0.007 |
| Tumor size* | |||
| Up to 2 cm | 1 | Reference | |
| 2–5 cm | 1.27 | 1.00–1.61 | 0.05 |
| Greater than 5 cm | 1.71 | 1.27–2.29 | <0.001 |
| T stage | |||
| T1 | 1 | Reference | |
| T2 | 1.53 | 1.28–1.83 | <0.001 |
| Biologic equivalent dose | |||
| <100 Gy | 1 | Reference | |
| ≥100 Gy | 0.69 | 0.58–0.83 | <0.001 |
| Propensity-matched | |||
| Type of radiotherapy | |||
| SBRT | 1 | Reference | |
| PBT | 0.48 | 0.29–0.78 | 0.003 |
| Biologic equivalent dose | |||
| <100 Gy | 1 | Reference | |
| ≥100 Gy | 0.61 | 0.38–0.98 | 0.04 |
*, tumor size and T stage analyses performed independently of each other given coverability. T stage based upon AJCC TNM staging manual. SBRT, stereotactic body radiation therapy; PBT, proton beam therapy; Gy, Gray; USD, United States Dollar.