Table 2.
Gafchromic EBT-2 Film Measurement of FWHM and 80% to 20% Penumbra at Different Depths for Various Collimators.
| Collimator | At Isocenter | At 18.6 mm Depth | At 37.2 mm Depth | |
|---|---|---|---|---|
| 0.5 mm diameter | FWHM (mm) | 0.47 | 0.54 | 0.61 |
| Penumbra (mm) | 0.2 ± 0.1 | 0.3 ± 0.1 | 0.3 ± 0.1 | |
| 1 mm diameter | FWHM (mm) | 1.14 | 1.18 | 1.2 |
| Penumbra (mm) | 0.3 ± 0.1 | 0.4 ± 0.1 | 0.5 ± 0.1 | |
| 2 × 2 mm2 | FWHM (mm) | 2.46 | 2.57 | 2.63 |
| Penumbra (mm) | 0.5 ± 0.1 | 0.58 ± 0.1 | 0.5 ± 0.1 | |
| 4 × 4 mm2 | FWHM (mm) | 4.48 | 4.81 | 5.01 |
| Penumbra (mm) | 0.5 ± 0.1 | 0.5 ± 0.1 | 0.6 ± 0.1 |
Abbreviation: FWHM, full-width half-maximum.