Table 3.
Ionization chamber measurements for verification of a single segmented field, with the dose gradient perpendicular to the direction of leaf motion
| Collimators following MLC | Collimators open | |||
|---|---|---|---|---|
| Position (cm) a | Calc. dose (cGy) | Difference (%) b | Calc. dose (cGy) | Difference (%) b |
| –4.2 | 159 | –3.4 (–2.2) | 167 | 2.3 (1.5) |
| –2.1 | 134 | –1.9 (–1.5) | 138 | –0.1 (–0.1) |
| 0 | 104 | –0.5 (–0.5) | 105 | 0.6 (0.6) |
| 2.1 | 71 | 0.4 (0.6) | 73 | 0.7 (1.1) |
| 4.2 | 37 | 0.5 (1.4) | 40 | 1.8 (5.1) |
a
Positions are relative to the central axis of the field, at 5 cm depth.
b
Dose differences are shown as a percentage of the central axis dose and as a percentage of local dose in parentheses.