Radioactive source localization employing resistive electrode array (REA) detector.

Objective.In this feasibility study, we explore an application of a Resistive Electrode Array (REA) for localization of a radioactive point source. The inverse problem posed by multichannel REA detection is studied from mathematical perspective and involves the questions of the minimal configuration of the conductive leads that can achieve this goal. The basic configuration consists of a circularly shaped REA with four opposite electrical lead-pairs at its perimeter.Approach.A robust mathematical reconstruction method for a 3D radioactive source relative to the REA is presented. The characteristic empirical Green's function for the detector response of the REA is determined by numerically solving Laplace equations with appropriate boundary conditions. Based on this model, Monte Carlo simulations of the inverse problem with Gaussian noise are performed and the overall accuracy of the localization is investigated.Main results.The results show a 3D error distribution of localization which is uniform in the (x,y)-plane of the REA and strongly correlated in the orthogonalz-axis. The overall accuracy decreases with higher distance of the source to the detector which is intuitive due to approximate flux dependence following the inverse square law. Further, a saturation in accuracy regarding the number of electrical leads and a linear dependence of the reconstruction error on the measurement noise level are observed.Significance.A broad range of REA detector configurations and their characteristics are investigated by this study for radioactive source localization allowing diverse practical applications with detector diameters ranging from millimeters to meters.

Resistive electrode array (REA) for radiotherapy beam monitoring and quality assurance.

We have developed a new type of detector array for monitoring of radiation beams in radiotherapy. The detector has parallel-plane architecture with multiple large-area uniform thin-film electrodes. At least one of the electrodes is resistive and has multiple signal readouts spread out along its perimeter. The integral dose deposited in the detector gives rise to multiple signals that depend on the distribution of radiation with respect to resistive electrode array (REA) geometry. The purpose of the present study was to experimentally determine basic detector response to MLC collimated x-ray fields. Two detector arrays have been characterized: circular and rectangular. The current and electrostatic potential distribution within the resistive electrode are governed by the Laplace and continuity equations with boundary conditions at the border with the readouts. Measurements for pencil beams showed that signal strength depends primarily on the distances between the location of the pencil beam and the readouts. Measurements for larger irregular MLC showed that signals as a function of time are quasi-linear with respect to MLC position and are proportional to the MLC area. Derivation of clinically relevant radiation beam parameters from REA signals, such as MLC position, MLC gap size and monitor unit per MLC segment relies on the detector response model with empirical model parameters. An approximate analytical detector response model was proposed and used to fit experiment data.