Seven29 Output Factors
The phantom material of solid phantoms is never really water-equivalent. Another problem is the lack of lateral scatter - solid phantoms have typical sizes of 30 cm x 30 cm, whereas large water phantoms are usually much larger.
On this page, output factors (one aspect of the problem of water-equivalence) for two setups are compared to the reference in water.
 |
 |
| Setup W: MP3 water phantom, 31003 chamber | Setup A: The 2D-ARRAY seven29 |
- Setup W uses the classical water phantom. A 0.3 ccm PTW ionization chamber (Type 31003) is aligned with isocenter. The chamber axis in 10 cm depth. The size of the water volume is 60 cm x 50 cm x 35 cm (PTW MP3).
- Setup A is the 2D-ARRAY under 9.5 cm of Solid Water (RW3). The SSD again is 90 cm. The inner side of the chamber entrance window is aligned with linac isocenter. Backscatter behind the ARRAY is 4 cm of RW3.
- Setup C uses the same 0.3 ccm chamber as in Setup W (chamber axis in isocenter, SSD 90 cm), with 10 cm of RW3 above and 5.7 cm of RW3 behind the chamber axis. The geometry is therefore comparable to Setup A.
For the three setups, the output factors relative to a 10x10cm field are measured for square field sizes between 3 cm x 3 cm and 27 cm x 27 cm. For Setup A (2D-ARRAY), the reading of the central axis chamber (#365) is taken.
Results 6MV
Output factors for 6MV, normalized to 10x10 field:
Differences for 6MV:
The numerical results for 6MV:
| Field [cm] | Setup W | Setup A | Setup C | A/W [%] | C/W [%] | A/C [%] |
|---|---|---|---|---|---|---|
| 3 | 0.8265 | 0.8311 | 0.8263 | +0.56 | -0.02 | 0.58 |
| 4 | 0.8628 | 0.8665 | 0.8655 | +0.43 | 0.31 | 0.12 |
| 6 | 0.9178 | 0.9216 | 0.9206 | +0.41 | 0.31 | 0.10 |
| 8 | 0.9638 | 0.9657 | 0.9649 | +0.19 | 0.11 | 0.08 |
| 10 | 1.0000 | 1.0000 | 1.0000 | 0.00 | 0.00 | 0.00 |
| 12 | 1.0294 | 1.0276 | 1.0279 | -0.17 | -0.14 | -0.03 |
| 15 | 1.0625 | 1.0583 | 1.0589 | -0.39 | -0.34 | -0.06 |
| 20 | 1.1027 | 1.0939 | 1.0957 | -0.80 | -0.64 | -0.16 |
| 25 | 1.1335 | 1.1199 | 1.1216 | -1.20 | -1.05 | -0.15 |
| 27 | 1.1442 | 1.1288 | 1.1301 | -1.35 | -1.23 | -0.12 |
Results 15MV
Output factors for 15MV, normalized to 10x10 field:
Differences for 15MV:
The numerical results for 15MV:
| Field [cm] | Setup W | Setup A | Setup C | A/W [%] | C/W [%] | A/C [%] |
|---|---|---|---|---|---|---|
| 3 | 0.8576 | 0.8687 | 0.8503 | +1.29 | -0.85 | 2.16 |
| 4 | 0.9010 | 0.9072 | 0.9008 | +0.68 | -0.03 | 0.71 |
| 6 | 0.9478 | 0.9504 | 0.9492 | +0.27 | 0.15 | 0.12 |
| 8 | 0.9784 | 0.9792 | 0.9785 | +0.09 | 0.01 | 0.07 |
| 10 | 1.0000 | 1.0000 | 1.0000 | 0.00 | 0.00 | 0.00 |
| 12 | 1.0176 | 1.0160 | 1.0162 | -0.15 | -0.13 | -0.02 |
| 15 | 1.0375 | 1.0338 | 1.0348 | -0.36 | -0.26 | -0.10 |
| 20 | 1.0628 | 1.0558 | 1.0572 | -0.66 | -0.54 | -0.12 |
| 25 | 1.0823 | 1.0720 | 1.0740 | -1.12 | -0.77 | -0.35 |
| 27 | 1.0896 | 1.0750 | 1.0792 | -1.34 | -0.95 | -0.39 |