Abstract
PurposeDosimetric properties of the new microSilicon diode detector (60023) have been studied with focus on application in small‐field dosimetry. The influences of the dimensions of the sensitive volume and the density of the epoxy layer surrounding the silicon chip of microSilicon have been quantified and compared to its predecessor (Diode E 60017) and the microDiamond (60019, all PTW‐Freiburg, Germany).MethodsDose linearity has been studied in the range from 0.01 to 8.55 Gy and dose‐per‐pulse dependence from 0.13 to 0.86 mGy/pulse. The effective point of measurement (EPOM) was determined by comparing measured percentage depth dose curves with a reference curve (Roos chamber). Output ratios were measured for nominal field sizes from 0.5 × 0.5 cm2 to 4 × 4 cm2. The corresponding small‐field output correction factors, k, were derived with a plastic scintillation detector as reference. The lateral dose–response function, K(x), was determined using a slit beam geometry.ResultsMicroSilicon shows linear dose response (R 2 = 1.000) in both low and high dose range up to 8.55 Gy with deviations of only up to 1% within the dose‐per‐pulse values investigated. The EPOM was found to lie (0.7 ± 0.2) mm below the front detector’s surface. The derived k for microSilicon (0.960 at s eff = 0.55 cm) is similar to that of microDiamond (0.956), while Diode E requires larger corrections (0.929). This improved behavior of microSilicon in small‐fields is reflected in the slightly wider K(x) compared to Diode E. Furthermore, the amplitude of the negative values in K(x) at the borders of the sensitive volume has been reduced.ConclusionsCompared to its predecessor, microSilicon shows improved dosimetric behavior with higher sensitivity and smaller dose‐per‐pulse dependence. Profile measurements demonstrated that microSilicon causes less perturbation in off‐axis measurements. It is especially suitable for the applications in small‐field output factors and profile measurements.
Highlights
Silicon diode detectors are generally used for dosimetric characterization of radiation beams, where high spatial resolutions are required, such as small-field output factor and profile measurements
Only detectors requiring less than 5% correction are recommended in the recently published TRS 483.7 In this study, it has been demonstrated that both the new microSilicon and the microDiamond fulfill this guideline down to the smallest investigated field size with seff = 0.55 cm, while the correction for the Diode E is larger than 5% in the two smallest field sizes investigated
The dosimetric properties of the new microSilicon detector have been characterized with focus on its application in small-field dosimetry
Summary
Silicon diode detectors are generally used for dosimetric characterization of radiation beams, where high spatial resolutions are required, such as small-field output factor and profile measurements. The sensitive volumes of most commercial silicon diode detectors have a diameter of around 1 mm, so that their signals are minimally perturbed by the geometrical volume-averaging effect.[1,2] the enhanced density detector’s components, such as the silicon chip and its surrounding layers, will cause these detectors to over-respond in small fields along the central axis. The silicon diode detector is known to over-respond in situations with increased contribution from low-energetic scattered photons due to the larger photo-effect interaction cross sections of silicon with Z = 14, as compared This socalled density effect is a result of the perturbation of secondary electrons’ fluence by the enhanced density components in situations where lateral secondary electrons equilibrium is not established.[3,4,5,6] the resulting small field output correction factors for silicon diode detectors are less than unity.[7]
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