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The Dosimetric Properties of a New Silicon Diode for Use in Small Field Dosimetry

A Ulrichs1*, D Poppinga2, R Kranzer2, B Poppe1, H Looe1, (1) University clinic for radiation physics, Pius Hospital, Medical Campus, University of Oldenburg, Oldenburg, Germany, (2) PTW Freiburg, Germany


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Diode detectors are used commonly for measurements requiring high spatial resolution. In this work, the dosimetric properties of a new silicon diode (microSilicon type 60023, PTW Freiburg, Germany) are investigated. The new diode is an updated version of the model 60017. The active layer has a diameter of 1.5 mm and the density of the grouting compound has been reduced to achieve a more water-equivalent dosimetric behavior. Dosimetric properties such as linearity, dose-per-pulse dependence (DPPD), effective point of measurement (EPOM) and the lateral dose response function K(x) are examined. Furthermore, its applicability in small fields was studied by performing profile and output ratio (OR) measurements.

Methods: Dose linearity and DPPD were investigated in comparison to an air-filled ionization chamber. The EPOM was obtained by comparing measured PDD curves with the reference curve obtained by using a Roos chamber. The function K(x) was determined according to the method introduced previously (Poppinga et al. PMB 2015). OR measurements were performed down to a field size length of 4 mm. By using a plastic scintillator as reference, the output factor correction factors were derived.

Results: The new diode shows a linear dose response (linear fit: R²=1.00) and no significant DPPD in the range of investigated dose rates. The K(x) has a full-width-half-maximum value of 0.992 mm and exhibits negative values beyond the boundaries of the sensitive volume due to the higher density detector’s component than water. Consequently, the output factor correction factors are smaller than unity for field sizes below 20 mm, whereby the new diode requires less correction (e.g. 0.960 at 5.5 mm) than its predecessor (e.g. 0.929 at 5.5 mm).

Conclusion: The new diode shows improved dosimetric characteristics over its predecessor for use in small field dosimetry exhibiting a smaller DPPD and requiring less corrections for small field OR measurements.

Funding Support, Disclosures, and Conflict of Interest: The study was funded by the ZIM project 'Entwicklung einer magnetfeldtauglichen Dosimetrie in der Strahlentherapie' of the German Ministry of Education and Research.


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