Figure 1
The example of shrinkage (right) of the head support.
Figure 2
Inter-fraction displacements by axis and period.
Table 1
Inter-fraction displacements recorded on units A and B at different periods
| 2014 Standard head support | 2015 Individual support | 2017 Individual support | |||||||
|---|---|---|---|---|---|---|---|---|---|
| VRT | LNG | LAT | VRT | LNG | LAT | VRT | LNG | LAT | |
| UNIT A | |||||||||
| Average displacement – M [mm] | - 0.86 | 0.05 | 0.05 | - 0.47* | - 0.24* | - 0.05 | - 0.16* | 0.88 | 0.18 |
| Systematic error – Σ [mm] | 0.66 | 1.04 | 0.88 | 0.91 | 0.79 | 0.95 | 0.82 | 0.59 | 0.83 |
| Random error – σ [mm] | 1.49 | 1.21 | 1.37 | 1.56 | 1.28 | 1.38 | 1.28 | 1.14 | 1.2 |
| UNIT B | |||||||||
| Average displacement – M [mm] | - 0.60 | 0.46 | - 0.43 | - 0.02* | 0.51 | 0.25 | - 0.18* | 0.46 | - 0.02 |
| Systematic error – Σ [mm] | 1.09 | 0.80 | 0.82 | 0.92 | 0.74 | 0.94 | 0.93 | 0.69 | 0.88 |
| Random error – σ [mm] | 1.77 | 1.83 | 1.47 | 1.77 | 1.22 | 1.41 | 1.71 | 1.56 | 1.44 |
Table 2
Number of IC displacements and of gross errors at treatment units in relation to time for both units. In the brackets, the most prevalent direction of applied movements is indicated
| Isocenter movements | ||||
|---|---|---|---|---|
| VRT | LNG | LAT | Gross errors | |
| Regression errors | ||||
| Unit A / unit B (direction) | Unit A / unit B (direction) | Unit A / unit B (direction) | ||
| 2014 – standard head support | 11 / 15 (P) | 5 / 15 (I) | 4 / 5 (L) | 2 / 5 |
| 2015 – individual head support | 12 / 13 (P) | 3 / 6 (I) | 9 / 8 (R) | 0 / 1 |
| 2017 – individual head support | 5 / 14 (P) | 7 / 10 (I) | 6 / 7 (L) | 0 / 1 |
Table 3
Clinical target volume - planning target volume (CTV-PTV) safety margins for units A and B at different periods (calculated according to van Herk8)
| CTV-PTV safety margin [mm] | |||
|---|---|---|---|
| VRT | LNG | LAT | |
| UNIT A | |||
| 2014 – standard head support | 2.7 | 3.4 | 3.2 |
| 2015 – individual head support | 3.4 | 2.9 | 3.3 |
| 2017 – individual head support | 2.9 | 2.3 | 2.9 |
| UNIT B | |||
| 2014 – standard head support | 4.0 | 3.3 | 3.1 |
| 2015 – individual head support | 3.5 | 2.7 | 3.3 |
| 2017 – individual head support | 3.5 | 2.8 | 3.2 |