Room: AAPM ePoster Library
The purpose of this study is the evaluation of the new microSilicon diode detector (PTW, Germany) for small field dosimetry by comparing with different detectors
This study was conducted using the linear accelerator Versa HD (Elekta, UK) that produces photon beams with 6 and 10 MV flattened filter(FF)/flattening filter free(FFF). Measurements of output factors and profiles were performed in water using four detectors (PTW microSiliocn, PTW60019 microDiamond, PTW31022 PinPoint 3D ionization chamber and PTW31021 SemiFlex 3D ionization chamber). The orientation of the detector is parallel to beam(axial) and, to consider the effective point of measurement, PTW TRUFIX system was used for all chambers. Profiles were measured at 90 cm SSD, 10 cm depth, and this setup was also used for relative output factor measurements.
In this work, we compared output factors of each detector for various square field sizes (reference field size: 10x10) (Figure 1.), and also compared field size(FWHM) from profile (Table 1) by the nominal field size. FWHM value was average values which of cross-plane and in-plane.
Figure 1 shows that relative output factors of each field sizes for all energies. The output factor for all detectors decreased with decreasing of field size. In small field (under 3x3 cm2), output factors measured by microDiamond and that by microSilicon are similar, and Pinpoint 3D and Semiflex 3D are similar. But, in 1x1cm2 field the difference of output factor between microDiamond and microSilicon is about 1.7 %. Generally, as the chamber volume increases, the FWHM becomes overestimate, but the difference between FWHM measured with microDiamond and microSilicon is less than 1 %.
For small field dosimetry, characterization of microSilicon diode detector are more similar to microDiamond detector than ionization chamber. But, under 1 x 1 cm2 field it is good to use with caution