Table 4.
Performance of cylinder phantom. Planned dose of 8 Gy delivered with single arcs of 2.4 × 5 mm2 fields, firstly with phantom positioned at isocenter, then at four different positions shifted by known distances from the previous positions. Applied shift distances along the three cardinal coordinate directions are shown in columns 2–4. Corresponding film measurements are shown in columns 5–7. Shift errors, defined as differences between measured and applied shifts are shown in the last three columns
| Shift # | Applied shift (mm) | Measured shift (mm) | Shift error (mm) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| x a | y a | z a | x m | y m | z m | Δx | Δy | Δz | |
| 1 | 0.20 | 0.20 | −0.20 | 0.26 | 0.24 | −0.15 | 0.06 | 0.04 | 0.05 |
| 2 | −0.40 | −0.40 | 0.40 | −0.36 | −0.44 | 0.38 | 0.04 | −0.04 | −0.02 |
| 3 | 0.20 | 0.20 | −0.20 | 0.21 | 0.17 | −0.26 | 0.01 | −0.03 | −0.06 |
| 4 | 0.30 | 0.00 | 0.00 | 0.27 | 0.00 | 0.04 | −0.03 | 0.00 | 0.04 |
| Average | 0.02 | −0.01 | 0.00 | ||||||
| Stdev. | 0.03 | 0.03 | 0.04 | ||||||
| Avg. error, all shifts | 0.005 | ||||||||
| Stdev., all shifts | 0.04 | ||||||||