Operating parameters of CVD diamond detectors for radiation dosimetry

A prototype clinical radiation detector based on commercially available single crystal diamond film made via chemical vapor deposition was investigated to determine optimal operating parameters for clinical dosimetry. This study examined how changes in applied electric field affected dosimetric performance, and determined a preferred operating voltage within the limits of clinical dosimetry equipment. Dosimetric analysis included leakage current, response dynamics such as rise and fall times, sensitivity, polarity and dependence on dose and dose rate. The results of this study indicate a preference for using a setting of 62.5 V due to its minimal rise time of 2 s, including a faster time to equilibrium, yet sufficient sensitivity of 37 nC Gy-1, which was nearly independent of polarity. At this voltage, a wider range of dose may therefore be recorded with charge collecting instruments than at higher voltages. Additionally, no clear trend was found over the range of voltages tested when evaluating dose dependence (R2=1 for 0.78-7.8 Gy) and dose rate dependence using Fowler fitting parameter Δ (0.95≤Δ≤1.01). Leakage currents were negligible (<2.5 pA). The highest voltage setting of 248.0 V resulted in the highest sensitivity of 235 nC Gy-1, but corresponding rise times of ≥7 s may limit the use of this detector. Following the optimization of operating parameters, clinical studies are ongoing to evaluate the use of this detector for small field and IMRT applications.