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Distance (in mm) between 20% and 80% of the maximum dose measured in the penumbral region for various modalities measured at 2 mm and 6 mm depth.
| 20-80% penumbra distance in millimeters | ||||||
|---|---|---|---|---|---|---|
| Depth | Ir 192 Photons | 6 MeV Electrons | 20 MeV Electrons | 6 MV Photons | 300 kVp Photons | 90 MeV Protons |
| 2 mm | 0.7 | 1.1 | 0.8 | 2 | 0.5 | 0.2 |
| 6 mm | 0.9 | 2.8 | 1.2 | 2.5 | 0.6 | 0.2 |
