A generic multimodule phantom for testing geometry of a linac c‐arm as a part of quality control in radiotherapy

Abstract

A concept of a multimodule multifiducial phantom has been introduced. Analytical framework has been developed to extract geometric characteristics of radiotherapy devices from projection images of a phantom. The phantom design and the methodology developed have been tested in simulations.

A simulation‐based method for evaluating geometric tests of a linac c‐arm in quality control in radiotherapy

“…In the simulations, we assume that all the subsystems of a simulated device are set correctly, that is, there is no difference between nominal and actual device settings like gantry or collimator angle, SDD, jaw positions, and other. Acquisition of images of a multimodule multifiducial phantom by an EPID is simulated using these nominal settings. The phantom consists of two modules, the first one, mounted on a treatment table, contains a set B = { B k : k = 1, 2, …, N B } of N B fiducial balls and the second one, mounted on a gantry head, contains a set C = { C l : l = 1, 2,..., N C } of N C fiducial balls …”

“…A generic procedure for a geometric test (e.g., the Winston‐Lutz test) consists of positioning of a special phantom containing one or more radiopaque fiducial markers in a radiation beam, acquisition of MeV images of the phantom (most frequently electronic portal imaging device (EPID) images) and then—based on dedicated image analysis methods—determination of the quantities of interest like isocenter position, source to detector distance (SDD) etc . Finally, the value of the geometric parameter as computed from the test results (e.g., EPID images) is compared against the assumed nominal value.…”

“…This paper is an extension of a previous work where a design of a multimodular phantom is presented and a set of reconstruction procedures for this phantom is briefly analyzed. In this paper, we focus on the problem of how the design of a geometric testing procedure and phantom influences the accuracy of estimation of parameters related to the geometry of linac C‐arms.…”

“…From this probability, one may infer if the device operates correctly or if there are other factors besides uncertainties in image acquisition (e.g., a malfunctioning subsystem of a linac) which account for the observed discrepancies between a nominal and an observed value of a geometric parameter under test. In the present paper, we consider geometry testing procedures based on a phantom proposed in an earlier paper, however the proposed approach can be applied to other phantoms described in the literature as well.…”

A Framework for Assumption-Free Assessment of Imperfect Geometry of a Linac C-Arms

“…The present paper is a continuation of our previous work [14], where one of possible phantom designs was proposed together with an optimization least-square method for assessment of various geometric characteristics (like isocenters) of EBT devices. We presented a method that can determine the geometry of a device using at least 13 parameters which, given three additional constraints, requires measuring the position in the detector plane of projections of at least 5 + 1 fiducial points in 3D space, the coordinates of which are exactly known (2 variables per point).…”