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Semi-conductor detectors in output factor measurements
M G Karlsson1, M Karlsson, R Sjögren
1Radiation Physics Department, Umeå University, Sweden.
Summary
Silicon diodes are suitable for small field output factor measurements, but cylindrical ionization chambers remain optimal for large fields. Diodes offer advantages in detector size and robustness for specific applications.
Area of Science:
- Medical Physics
- Radiation Oncology
- Detector Technology
Background:
- Output factors are crucial in radiation therapy dose calculations.
- Cylindrical ionization chambers are the standard for these measurements.
- Alternative detectors like silicon diodes are being explored for their potential advantages.
Purpose of the Study:
- To evaluate the suitability of p-type silicon diodes for output factor measurements.
- To compare diode performance against traditional ionization chambers.
- To assess the impact of detector size and construction on measurement accuracy.
Main Methods:
- Two types of silicon diodes (shielded and standard) were tested.
- Measurements were conducted across various accelerating potentials (4-50 MV) and beam sizes (4x4 cm to 40x40 cm).
- Evaluations included head scatter factors in mini-phantoms and output factors in extended water phantoms.
Main Results:
- Both diode types proved effective for head scatter factor measurements in mini-phantoms.
- Diodes were found unsuitable for large field output factor measurements in extended phantoms.
- For small fields (<10x10 cm), diodes showed advantages due to their small size, with no scatter-related errors observed.
Conclusions:
- Cylindrical ionization chambers are preferred for large field output factor measurements in extended water phantoms.
- Silicon diodes are a viable alternative for output factor measurements in small radiation fields.
- Minimal differences were noted between diode types for head scatter measurements in mini-phantoms.