Background
Methods
Construction of the PMMA phantom
Measurement of absorbed dose to water
Monte Carlo simulation of the scattering contribution
Measurement of the beam profile
Results
Construction of the PMMA phantom
Component | fi | Z/A | ρe,PMMA | ρe,PMMA /ρe,water |
---|---|---|---|---|
H | 0.081 | 0.992162 | 0.639 | 1.155 |
C | 0.595 | 0.499542 | ||
O | 0.317 | 0.500031 | ||
unknown | 0.007 | 0.500 |
Measurement of absorbed dose rate to water
Measurement of the beam profile
FWHM (mm) | Penumbra (mm) | |||||||
---|---|---|---|---|---|---|---|---|
Axis | PMMA | LGP6.93a | SW | LGP8.0b | PMMA | LGP6.93a | SW | LGP8.0b |
x | 21.83 ± 0.25 | 21.68 | 21.57 ± 0.27 | 21.75 | 9.58 ± 0.22 | 9.04 | 8.76 ± 0.19 | 9.03 |
y | 22.10 ± 0.32 | 21.68 | 21.56 ± 0.27 | 21.75 | 9.86 ± 0.18 | 9.04 | 8.96 ± 0.23 | 9.03 |
z | 17.46 ± 0.11 | 17.39 | 17.41 ± 0.17 | 17.44 | 2.72 ± 0.10 | 3.09 | 2.65 ± 0.14 | 2.55 |
Discussion
Measurement of the absorbed dose rate to water
Measurement of the beam profile
Uncertainty analysis
Uncertainty component | Type A (%) | Type B (%) |
---|---|---|
Calibration factor of the ionization chamber, \( {N}_{D_w,{Q}_0}^c \) | 0.50 | |
Ionization current measurement | 0.01 | 0.02 |
Temperature and pressure measurement | 0.056 | |
Scattered photon contribution | 0.01 | 1.28 |
Displacement of the ionization chamber | 0.01 | 0.15 |
Alignment of the PMMA phantom with the PPS calibration center | 0.20 | |
Long-term stability of the ionization chamber | 0.12 | |
Standard relative combined uncertainty | 1.40 |
Uncertainty component | Type A (%) | Type B (%) |
---|---|---|
Optical density measurement | 0.10 | 0.02 |
Intensity resolution | 0.002 | |
Uniformity of the radiochromic film | 0.50 | |
Temperature and relative humidity measurements | 0.056 | |
Alignment of the PMMA phantom with the PPS calibration center | 0.20 | |
Positioning of the radiochromic film inside the phantom | 0.16 | |
Calibration curve fitting | 1.33 | |
Measurements of FWHM and penumbra | 0.02 | 0.01 |
Standard relative combined uncertainty | 1.45 |