Quantitative assessment of quality of digitized portal images: receiver operating characteristic analysis applied to imaging in radiation therapy.

Abstract

An objective and quantitative method for the evaluation of the quality of megavoltage portal images was developed by applying receiver operating characteristic analysis. On the basis of therapeutic use of portal images, setup errors were employed as "signals" in this experimental study that compared the original portal films with digitized images. Six readers observed 104 portal images of a chest phantom, half of which were "abnormal" (ie, had setup errors). Digital images (2,048 x 2,048 matrix) were enhanced by means of histogram equalization and then printed with a laser printer for observation. The readers showed a higher discrimination capacity with the digitally enhanced images, although a statistically significant improvement was not demonstrated. The present method of assessment of image quality proved to be both simple and clinically reasonable.

Advances in an Interdisciplinary Science

“…In comparison with the clinical evidence, the system proved to be correct in 72% of the cases. The authors conclude correctly that their method requires a more extensive evaluation and a presentation of the results by ROCs (as was done in the studies by Deller et al [28], Okajima et al [23], Willems et al [27], and Tahoces et al [35]). Given the high incidence of breast cancer, even a slight improvement of diagnostic accuracy would be of great help which should also be balanced against costs.…”

“…The following two publications are on the use of computers to assist people with physical handicaps, dysarthric speech and impaired vision, respectively. The last article by Okajima et al [23] is on the quality assessment of portal images for the preparation of radiation therapy.…”

“…The last publication in this section is devoted to a subject which is different from the others; the study by Okajima et al [23] has compared portal images with and without con-trast enhancement, in some way comparable to the study by Peli et al [29], but for an entirely different purpose, i. e., the preparation of patients for radiation therapy. In that sense, this article could also have been categorized under the next section on image and signal processing.…”

“…The pictures appear to be sharper for diagnostic interpretation; especially microcalcifications in mammograms are better visualized. However, no diagnostic assessment was done, e. g., by ROC analysis, as in Okajima's study [23] in section 2. The processing takes a minimal amount of time so that it is well suitable for fully automatic routine implementation.…”

Optimal specifications for beam calibration checks in radiotherapy calculated with gauge repeatability and reproducibility, and sensitivity and specificity studies

“…This calculation can be linked to the theory of detection (Peterson et al 1954, Swets et al 1961, Metz 2008) via the concepts of sensitivity and specificity and receiver operating characteristic (ROC) curves (Metz 1978) which are also applied to clinical medicine (Lusted 1971, Swets 1988) and radiology (Swets 1979, Metz 1986, 1989. In the field of radiotherapy, ROC analysis has also been used to assess related computeraided diagnoses (Mizowaki et al 1996), evaluate image equipment (Okajima et al 1991) and segmentation algorithms (Barrett et al 2010), study the quality of plans (Platoni et al 1999), and optimize treatments and clinical outcomes (Andrews 1985, Lind et al 2002, Mavroidis et al 2003, Lind et al 2006. Currently, sensitivity and specificity calculations are also recommended for controlling the quality of intensitymodulated radiotherapy treatments (Carlone et al 2013, Gordon and Siebers 2013, McKenzie et al 2014.…”