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

Abstract

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.

Radioactive source localization employing resistive electrode array (REA) detector

“…Detector response model for a single injection point 2.2.1. Physics of the signal generation Dose (energy deposited per unit mass of the active volume of the detector) at given location (x, y, z = 0) of the detector generates charges that are injected into (or induced in) the resistive electrode at a rate that is proportional to the dose rate [1]. Therefore, the total detector response is an integral of detector responses for a pointwise current injections over the whole area of the RE.…”

“…Therefore, the total detector response is an integral of detector responses for a pointwise current injections over the whole area of the RE. This model can be conceived as a Green's function approach in which the radiation flux f (x, y, z = 0) is multiplied by the detector response (Green's function) at that point for a specific location of source and DAQ points at the edge of the normalized disk cos , sin 1 1 q q ( ( ) ( ))and cos , sin q q ( ( ) ( )). The following formulae describe the relation between the electrical potential Φ(x, y), electric field E (x, y) vector and current density j(x, y) in the plane of the resitive electrode (x,y):…”

“…A new type of radiation detector Resistive Electrode Array (REA) has been developed and experimentally characterized in megavoltage x-rays beams produced by a medical linear accelerator [1]. The main feature of REA is that it is a large area flat thin film or thin panel detector possessing at least one large electrode with multiple conductive leads at its edges.…”

“…A general REA device [1] has been proposed with flexible sensor architectures to allow for different configurations matching the application needs, including: the number of leads attached at the perimeter of the resistive electrode (and therefore the number of data acquisition channels), their specific distribution (at equal distances or different distances from each other for the adjacent leads). In the prototypical REA devices used to monitor megavoltage x-ray beams from a medical linear accelerator, there were two architectures adopted: a circular resistive electrode with 24 evenly spaced leads, and a rectangular resistive electrode with 2 opposing arrays of 8 evenly spaced leads on 2 opposing sides and the other sides without any leads [1]. In these prototypical REA detectors energy conversion has been realized via a parallel plate ion chamber design [1].…”

“…In the prototypical REA devices used to monitor megavoltage x-ray beams from a medical linear accelerator, there were two architectures adopted: a circular resistive electrode with 24 evenly spaced leads, and a rectangular resistive electrode with 2 opposing arrays of 8 evenly spaced leads on 2 opposing sides and the other sides without any leads [1]. In these prototypical REA detectors energy conversion has been realized via a parallel plate ion chamber design [1]. However, in principle other energy conversion schemes are possible based on photosensitive thin films [2,3] or High Energy Current (HEC) structures [4].…”