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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