Table 2.
Ionization chamber measurements for verification of a single segmented field, with the dose gradient parallel 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 | 163 | –4.4 (–2.8) | 167 | 1.2 (0.8) |
| –2.1 | 134 | –4.7 (–3.5) | 138 | –0.7 (–0.6) |
| 0 | 101 | –3.3 (–3.3) | 105 | –0.1 (–0.1) |
| 2.1 | 69 | –2.7 (–3.9) | 73 | –0.1 (–0.2) |
| 4.2 | 36 | –1.5 (–4.3) | 40 | 0.6 (1.6) |
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.