(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: The aim of this work is to investigate the response of various two-dimensional detector arrays with respect to the mean photon energy Em under non-reference conditions.
Methods: The OCTAVIUS 1500 and the OCTAVIUS 729 with vented ionization chambers, the OCTAVIUS 1000SRS (all PTW-Freiburg) with liquid-filled ionization chambers and the MapCHECK2 (Sun Nuclear) with silicon diodes were investigated.The relative response M_array of the central detector of each 2D-array was measured at different depths (d=2 cm to 20 cm) and for different nominal field sizes (4 x 4 cm² to 20 x 20 cm²) in water equivalent plastic (RW3). The readings of a PTW Semiflex 31010 detector were corrected for their energy dependence and used as reference measurement M_ref. All measurements were carried out at SSD=100 cm and normalized to the reference field (d=10 cm, 10 x 10 cm²). Measurements were performed at a Siemens ARTISTE linac using 6 MV photon beam. The energy dependence of each 2D-array was estimated by calculating the maximum variation of M_ref / M_array. The mean photon energies Em at each point of measurement were simulated using the EGSnrc 2017 software.
Results: For the investigated field sizes and measurement depths, the simulated Em ranges from 0.89 to 1.844 MeV. For the vented OCTAVIUS 729 and OCTAVIUS 1500 detectors the maximum variation in response is 0.85% and 1.3% respectively. The OCTAVIUS 1000SRS shows a maximum variation in response of 1.41%, while the MapCHECK2 Si-diode exhibits a maximum variation of 1.58%.
Conclusion: None of the investigated 2D-arrays exhibits energy response variations bigger than 2% within the investigated energy range along the beam’s central axis. Vented ionization chambers show in general smaller energy dependence compared to diodes and liquid-filled ionization chambers.
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