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

Abstract

Purpose Assessment of the accuracy of geometric tests of a linac used in external beam therapy is crucial for ensuring precise dose delivery. In this paper, a new simulation‐based method for assessing accuracy of such geometric tests is proposed and evaluated on a set of testing procedures. Methods Linac geometry testing methods used in this study are based on an established design of a two‐module phantom. Electronic portal imaging device (EPID) images of fiducial balls contained in these modules can be used to automatically reconstruct linac geometry. The projection of the phantom modules fiducial balls onto the EPID detector plane is simulated for assumed nominal geometry of a linac. Then, random errors are added to the coordinates of the projections of the centers of the fiducial balls and the linac geometry is reconstructed from these data. Results Reconstruction is performed for a set of geometric test designs and it is shown how the dispersion of the reconstructed values of geometric parameters depends on the design of a geometric test. Assuming realistic accuracy of EPID image analysis, it is shown that for selected testing plans the reconstruction accuracy of geometric parameters can be significantly better than commonly used action thresholds for these parameters. Conclusions Proposed solution has the potential to improve geometric testing design and practice. It is an important part of a fully automated geometric testing solution.

Are gamma passing rate and dose–volume histogram QA metrics correlated?

“…To systematically evaluate the contribution of errors which affect the quality of delivery of a radiotherapy plan, QA procedures are usually applied at three consecutive levels: a level to address the geometry and performance of the medical accelerator with its accessories [1][2][3][4] -as controlled by the TPS, and the performance of the TPS itself, 5 a level to address individual patient issues prior to acceptance of a dose delivery plan, [5][6][7] and finally one to address the actual course of radiotherapy (such as patient set-up, or inter-and intrafraction patient positioning and anatomy changes).…”

A Set Theory- And ROC-Based Patient-Specific QA Measure To Compare Planned And Delivered Isodose Distributions In Photon Radiotherapy

“…Advances in radiotherapy are reflected in increasingly complex tests of commissioning, therapy planning, onboard imaging, beam geometry, or beam delivery systems [1][2][3][4][5], and of dosimetry tools [6]. Among such tests, patientspecific procedures [1,2,7,8] remain the core component of clinical quality assurance (QA).…”