Table 2.
Backscatter factor ratio and measured dose rate ratio. The variation of the dose rate as a function of the field diameter is basically due to the variation in the backscatter produced when photons interact with the solid water.
| Field diameter (cm) | AAPM TG-61 backscattera | Backscatter ratio (normalized to the field diameter of 1 cm) | Measured dose rate ratio (normalized to the field diameter of 1 cm) |
|---|---|---|---|
| 5.0 | 1.242 | 0.852 | 0.832 |
| 2.0 | 1.120 | 0.945 | 0.945 |
| 1.0 | 1.059 | 1 | 1 |
a
Backscatter factors for a HVL = 5.6 mmAl and a source–surface distance of 35.4 cm.