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18 MV X-rays
Physical quantity of procedure
Relative standard uncertainty (%)
OneDosePlus
MOSFET
(T&N)
diode
Step 1: Calibration under reference conditions
Dose measured with the ionisation chamber
2.0%
2.0%
2.0%
Reading of the in vivo detector
2.6%
0.7%
0.1%
Reproducibility of the setting
0.5%
0.3%
Combined standard uncertainty of step 1
3.3%
2.2%
2.0%
Step 2: Correction factors
Field correction factor
3.0%
0.8%
0.1%
SSD correction factor
2.0%
0.8%
0.2%
Combined standard uncertainty of step 2
3.6%
1.1%
0.2%
Step 3: measure on the patient
Reading of the in vivo detector
1
3.3%
0.7%
0.1%
Combined standard uncertainty of step 3
3.3%
0.7%
0.1%
Combined standard uncertainty of steps 1+2+3
5.9%
2.6%
2.0%
1
reproducibility on positioning on patients was not tested.
Uncertainty in entrance dose measurements