Dose Course 2018_Flipping book

Uncertainty in entrance dose measurements

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% 2.6%

2.0% 0.7% 0.5% 2.2%

2.0% 0.1% 0.3% 2.0%

Reading of the in vivo detector Reproducibility of the setting

Combined standard uncertainty of step 1

3.3%

Step 2: Correction factors Field correction factor

3.0% 2.0% 3.6%

0.8% 0.8% 1.1%

0.1% 0.2% 0.2%

SSD correction factor

Combined standard uncertainty of step 2

Step 3: measure on the patient Reading of the in vivo detector 1

3.3% 3.3%

0.7% 0.7%

0.1% 0.1%

Combined standard uncertainty of step 3

Combined standard uncertainty of steps 1+2+3

5.9%

2.6%

2.0%

1 reproducibility on positioning on patients was not tested.