Table 4.
Dose comparisons of the first and second CBCT images.
| Mean dose (Gy) | Maximal dose (Gy) | |||||||
|---|---|---|---|---|---|---|---|---|
| GTV | CTV | PTV | Left-parotid | Right-parotid | Brain-stem | Spinal-cord | Whole-body | |
| kV CT | 50.72 | 51.04 | 51.02 | 32.14 | 30.40 | 50.92 | 31.76 | 55.78 |
| 1st kV CBCT | 50.23 | 50.77 | 50.74 | 31.88 | 30.57 | 51.21 | 31.17 | 55.63 |
| Dose difference between 1st kV CBCT and kV CT(%) | 0.98% | 0.54% | 0.54% | 0.8% | -0.56% | 0.57% | -1.87% | -0.26% |
| 2nd kV CBCT | 50.37 | 50.77 | 50.76 | 32.56 | 28.73 | 51.36 | 32.96 | 55.71 |
| Dose difference between 2nd kV CBCT and kV CT(%) | 0.7% | 0.53% | 0.52% | -1.3% | 5.81% | 0.86% | 3.77% | -0.11% |
Dose comparison of the first and second CBCTs to the reference planning kVCT in a patient (patient 4) with marked anatomical changes. The largest changes in dose difference between CBCT and planning CT are found in the spinal cord (from -1.87% to 3.77%) and in the right parotid (from -0.56% to 5.81%).