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GEOMETRICAL EFFICIENCY OF PLANE-PARALLEL IONIZATION CHAMBERS IN PROTON SCANNING BEAM
N Mojzeszek1, M Klodowska1, W Komenda1
1Institute of Nuclear Physics PAN (IFJ PAN), Radzikowskiego 152, Kraków, Poland.
Radiation Protection Dosimetry
|October 18, 2017
Summary
Accurate proton therapy requires precise depth dose measurements. This study quantifies ionization chamber geometrical efficiency, crucial for integral depth dose acquisition in pencil beam scanning, finding optimal efficiency at lower energies.
Area of Science:
- Medical Physics
- Radiation Oncology
- Particle Therapy
Background:
- Proton therapy commissioning requires accurate depth dose distributions for treatment planning.
- Pencil beam scanning (PBS) necessitates integral depth dose (IDD) acquisition using detectors that account for beam broadening due to scattered and secondary particles.
Purpose of the Study:
- To quantify the geometrical efficiency of ionization chambers (ICs) based on their radius and proton beam energy.
- To assess the impact of IC size and proton energy on IDD measurements in PBS.
- To provide data for optimizing detector selection in proton therapy commissioning.
Main Methods:
- Utilized a combination of experimental measurements and Monte Carlo transport calculations.
- Investigated the geometrical efficiency of ionization chambers with different radii (4.08 cm and 6 cm).
- Evaluated efficiency across a range of proton beam energies, including up to 226.08 MeV.
Main Results:
- Achieved a geometrical efficiency of 0.99 for ICs with 4.08 cm and 6 cm radii at proton energies up to 160 and 190 MeV.
- Observed significantly lower geometrical efficiency at 226.08 MeV, resulting in charge losses of 5.8% (4.08 cm IC) and 3.6% (6 cm IC).
- Relative IDD differences between the two IC sizes increased with proton energy, reaching 2.4% at mid-range depth for 226.08 MeV.
Conclusions:
- Ionization chamber geometrical efficiency is energy-dependent, particularly at higher proton beam energies.
- Detector size plays a critical role in IDD accuracy, with larger discrepancies at higher energies.
- Careful selection of ionization chamber size and consideration of energy-dependent efficiency are essential for accurate proton therapy commissioning.