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Characteristics and Effective Point of Measurement of a MicroSilicon Detector in Electron Beam Dosimetry

I Das1*, S Srivastava2, (1) Northwestern University Medical Center, Chicago, IL, (2) University of Arizona Cancer Center, Chandler, AZ

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Silicon solid state detectors are suitable for electron depth dose and profile measurements as they do not require stopping power correction at depth unlike ion chambers where percent ionization needs to be converted to depth dose based on stopping power ratio. Recently, a new microSilicon (µSi) unshielded diode detector PTW-60023 was introduced and commercially available for small photon field dosimetry. The detector has 1.5 mm diameter disk with 18µm thickness. Akino provided comprehensive data on this detector, including, dose, dose rate, energy, PDD. However temporal and effective point of measurement and cone factors were not discussed which is provided in this study.
Methods: Measurements were performed on a Varian TrueBeam with 6-16 MeV electrons. Temporal response was performed with 100 MU repeated over an interval of time. The depth dose was measured from depth in water into air. The data were fitted as described (Das, PMB, 1998). Output factors were measured for all energies in water and compared with ion chamber data.
Results: Our results show that µSi detector is independent of the temporal response. The effective point was determined to be 0.5±0.2 mm from the manufacturer marked line in electron beam. Once the shift is applied the depth dose matches perfectly within 1.5% to ion chamber and PTW-60012 silicon detector. The measured cone factors are identical (±1.2%) to the values with ion chamber.
Conclusion: µSi is a very suitable detector with dose, dose rate, energy, temporal independence. The effective point of measurement was determined to be 0.5±0.2 mm upward of the manufacturer defined line on the detector in electron beam whereas it is 0.7 ±0.2 mm in photon beam. Based on the characteristics of this detector, it is an ideal detector for electron beam dosimetry that does not require any correction and can be used for small field.

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