Table 2.
Dosimetric parameters and MUs of VMAT plans with intersection angle of two collimators (Δθ) changing from 20° to 90°, along with their Friedman test results.
| Parameter | Result for VMAT with collimator angles θ1/θ2 a | p-value | |||||
|---|---|---|---|---|---|---|---|
| 350°/10° | 350°/30° | 350°/45° | 350°/60° | 350°/80° | |||
| PTV | CI | 0.848 ± 0.009 | 0.853 ± 0.007 | 0.856 ± 0.007 | 0.858 ± 0.004 | 0.857 ± 0.008 | 0.002* |
| HI | 0.259 ± 0.023 | 0.212 ± 0.016 | 0.202 ± 0.016 | 0.199 ± 0.012 | 0.194 ± 0.019 | < 0.001* | |
| Hippocampus | D100% (cGy) | 929.7 ± 40.1 | 891.1 ± 32.8 | 884.2 ± 25.1 | 880.5 ± 31.7 | 878.8 ± 29.2 | < 0.001* |
| Dmax (cGy) | 1507.2 ± 105.6 | 1433.0 ± 77.7 | 1422.0 ± 65.7 | 1434.2 ± 76.7 | 1412.7 ± 79.3 | < 0.001* | |
| Dmean (cGy) | 1103.3 ± 43.3 | 1056.5 ± 31.0 | 1053.8 ± 27.6 | 1049.6 ± 29.7 | 1043.3 ± 30.3 | < 0.001* | |
| Inner ear | Dmean (cGy) | 1437.6 ± 40.3 | 1433.0 ± 20.1 | 1429.5 ± 30.0 | 1427.4 ± 29.8 | 1427.3 ± 29.1 | 0.008* |
| Lens | Dmax (cGy) | 705.3 ± 29.3 | 697.2 ± 33.3 | 705.5 ± 32.6 | 703.6 ± 24.7 | 702.4 ± 38.1 | 0.699 |
| Optical nerve | Dmax (cGy) | 3143.5 ± 156.3 | 3106.8 ± 118.2 | 3175.1 ± 40.4 | 3123.6 ± 103.1 | 3087.3 ± 127.0 | 0.053 |
| Eye | Dmean (cGy) | 970.9 ± 37.5 | 943.2 ± 18.3 | 934.0 ± 17.6 | 930.5 ± 11.6 | 921.0 ± 20.9 | < 0.001* |
| Monitor Unit | MU | 1073.6 ± 118.8 | 929.5 ± 44.6 | 908.7 ± 33.9 | 900.6 ± 28.5 | 899.5 ± 28.2 | < 0.001* |
aθ1 and θ2 indicate the collimator angles of arc 1 and arc 2, respectively.
*Statistically significant (p < 0.05).