Characterization of an “Edgeless” Dosimeter for Angular Independent Measurements in Advanced Radiotherapy Treatments

In this paper, the performance of an “edgeless” device is evaluated for use as an angular independent detector for dosimetric quality assurance in radiotherapy. The edgeless diodes were tested in terms of current-voltage (IV) and capacitance- voltage (CV) characteristics, charge collection efficiency and radiation hardness. A model of the edgeless device was developed to simulate the distribution of the electric field for different geometries using technology computer aided design (TCAD). IV and CV characteristics of the diodes indicate the appropriate operational conditions and provide a means to assess the consistency/quality of the edgeless diode technology. TCAD model shows good agreement with experimental results demonstrating the accuracy of the model in simulating the behavior of the edgeless diodes. The charge collection efficiency is evaluated for two of the edgeless configurations PP and NP. The angular dependence measurements of edgeless devices before and after 2 Mrad irradiation shows negligible effect of radiation damage on response as a function of the angle. The experimental data are supported by the results of the TCAD simulation study, which indicates negligible impact of radiation damage from a clinical use perspective. Both the experimental and simulated results derived from the radiation damage study show minimal degradation (within 4%) of the diodes sensitivity.