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On the Dose Response Function and the Energy Dependence of a Novel Synthetic Single Crystal Diamond Detector

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H Looe

H K Looe1,2*, N Chofor1,2, A Harmeyer1,2, D Poppinga1,2, A Schoenfeld1,2, D Grabowski1,2, K Willborn2, D Harder3, B Poppe1,2, (1) WG Medical Radiation Physics, Carl von Ossietzky University, Oldenburg, Germany (2) Clinic for Radiotherapy, Pius-Hospital, Oldenburg, Germany (3) University of Goettingen, Germany

SU-E-T-65 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To characterize the dose response function K(x) and to analyze the dependence on changing photon spectra of a novel synthetic single crystal diamond prototype detector (microDiamond, T60019, PTW-Freiburg).

Methods: The K(x) of the microDiamond was examined by scanning a narrow photon field, with the detector symmetry axis arranged towards the photon source, at 6 and 15 MV. The same dose profiles were scanned with a Si diode, for which the K(x) is already known, to obtain D(x). In a search process, the D(x) were numerically convolved with normalized one-dimensional Gaussian kernels K(x) of varying σ. The best fit between the convolution product D(x) * K(x) and the measured profile M(x) of the microDiamond was used to determine σ. Furthermore, profiles were compared with ion-chamber (PTW Semiflex 31010) measurements at different field sizes and depths to study its spatial resolution, output factor and out-of-field measurement characteristics. The EPOM was determined by comparing the PDDs against those obtained with a Roos chamber.

Results: The optimal σ of K(x) of the microDiamond was found to be 1.14 mm, which is comparable to the detector dimensions (radius = 1.1 mm). The microDiamond profiles agree well with the ion-chamber measurements within regions where the volume effect of the ion-chamber can be neglected. At 10 cm depth and for field sizes between 4x4 cm² and 20x20 cm² the output factors measured with the microDiamond and ion-chamber agree better than 1% thus setting a limit for a possible energy dependence of the detector. This is underpinned by the good agreement of the out-of field doses between ion-chamber and microDiamond. The vendor specified EPOM was also verified (1.3 mm below the surface).

Conclusion: Our study indicates that the characteristics of the microDiamond detector are well suited for accurate dosimetry within the investigated field sizes and depth limits.

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