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Reversing the Bias Against Diodes: Instantaneous Dose Rate Corrections to Improve Scanning Performance

S Graves*, D Hyer , University Of Iowa, Iowa City, IA


(Sunday, 7/29/2018) 4:00 PM - 5:00 PM

Room: Exhibit Hall | Forum 3

Purpose: Characteristics of diode detectors which are favorable include their low manufacturing cost, small active volume, and high signal-to-noise ratio. Although these attributes make diodes attractive for relative dosimetry measurements, adoption of diode detectors for depth-dose measurements has been limited due to concerns regarding response variability as a function of energy and instantaneous dose rate. The purpose of this work was to evaluate the feasibility of measuring and correcting for the instantaneous dose rate response dependence of a diode detector.

Methods: A diode detector (SNC EDGE-detector) and ionization chamber (0.125cc, PTW-TN31010) were placed under brass build-up caps and suspended in air. Detectors were were irradiated by 6MV photons at varying distances (thereby varying instantaneous dose rates). The ratio of the measured diode response to the corrected chamber response as a function of instantaneous dose rate was fit by a power model previously described in literature (Sainai, Zhu, Med. Phys., 2004). This instantaneous dose rate was applied to varying depth-dose scans taken in water taken using the diode detector, and the resulting data was compared against scans taken using an ionization chamber.

Results: The diode detector was found to over-respond with increasing dose rate, as expected. The analytic model closely matched the measured data (Χ²/df=0.35) and was successfully used for response correction in measured depth-dose scanning data using the same diode detector. The magnitude of correction was approximately 1.5% at 10 cm depth for 6MV and 6FFF beams. Deviation from ground-truth (correction chamber readings) was found to improve for field sizes of 5x5 and smaller, but above these field sizes spectral effects dominated the difference in readings between the ion chamber and diode.

Conclusion: Methods for measurement and correction of the instantaneous dose-rate dependence for diode detectors were successfully established and employed. These techniques may prove useful in small-field dosimetry applications.


Diodes, Dosimetry, Small Fields


TH- External beam- photons: Small/nonstandard field experimental dosimetry

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