Quality parameter of photon beam
During acceptance tests for the treatment unit depth-dose curves are measured (usually for fixed SSD).
Parameter D10/D20 i.e. ratio of doses at depths 10 and 20 cm for field size 10cm x 10cm describes the beam quality.Experimental data for SSD=100 cm
...and values as follows:
|
D10/20 |
MV |
|
2.20 |
2.0 |
|
2.07 |
2.5 |
|
1.98 |
3.0 |
|
1.90 |
3.5 |
|
1.84 |
4.0 |
|
1.80 |
4.5 |
|
1.77 |
5.0 |
|
1.71 |
6.0 |
|
1.67 |
7.0 |
|
1.64 |
8.0 |
|
1.62 |
9.0 |
|
1.59 |
10.0 |
|
1.56 |
12.0 |
|
1.54 |
14.0 |
|
1.52 |
16.0 |
|
1.50 |
19.0 |
|
1.47 |
25.0 |
|
1.46 |
30.0 |
|
1.42 |
50.0 |