Assessment of Interobserver Reproducibility in Quantitative ¹⁸F-FDG PET and CT Measurements of Tumor Response to Therapy

Abstract

Our goal was to estimate and compare across different readers the reproducibility of the 18 F-FDG PET standardized uptake value (SUV) and CT size measurements, and changes in those measurements, in malignant tumors before and after therapy. Methods: Fifty-two tumors in 25 patients were evaluated on 18 F-FDG PET/CT scans. Maximum SUVs (SUV bw max) and CT size measurements were determined for each tumor independently on pre-and posttreatment scans by 8 different readers (4 PET, 4 CT) using routine nonautomated clinical methods. Percentage changes in SUV bw max and CT size between pre-and posttreatment scans were calculated. Interobserver reproducibility of SUV bw max, CT size, and changes in these values were described by intraclass correlation coefficients (ICCs) and estimates of variance. Results: The ICC was higher for the pretreatment, posttreatment, and percentage change in SUV bw max than the ICC for the longest CT size and the 2-dimensional CT size (before treatment, 0.93, 0.72, and 0.61, respectively; after treatment, 0.91, 0.85, and 0.45, respectively; and percentage change, 0.94, 0.70, and 0.33, respectively). The variability of SUV bw max was significantly lower than the variability of the longest CT size and the 2-dimensional CT size (mean 6 SD before treatment, 6.3% 6 14.2%, 16.2% 6 17.8%, and 27.5% 6 26.7%, respectively, P # 0.001; and after treatment, 18.4% 6 26.8%, 35.1% 6 47.5%, and 50.9% 6 51.4%, respectively, P # 0.02). The variability of percentage change in SUV bw max (16.7% 6 36.2%) was significantly lower than that for percentage change in the longest CT size (156.3% 6 157.3%, P # 0.0001) and the 2-dimensional CT size (178.4% 6 546.5%, P , 0.0001). Conclusion: The interobserver reproducibility of SUV bw max for both untreated and treated tumors and percentage change in SUV bw max are substantially higher than measurements of CT size and percentage change in CT size. Measurements of tumor metabolism by PET should be included in trials to assess response to therapy.Although PET reproducibility was high, the variability observed in analyses of identical image sets by 4 readers indicates that automated analytic tools to assess response might be helpful to further enhance reproducibility.

Repeatability of SUV in Oncologic 18F-FDG PET

“…Although relevant, these studies are not expected to be directly comparable to human studies, which were the main interest. Also excluded were studies that involved repeated imaging after a single 18 F-FDG administration (18), studies that measured the repeatability of different readers analyzing the same images (19), and repeatability studies that did not include SUV quantification. Table 1 shows the articles that were identified and included in this review.…”

Quantitation of Cancer Treatment Response by 18F-FDG PET/CT: Multicenter Assessment of Measurement Variability

“…The ability of multiple readers to assign the same treatment response is to some extent dependent on the repeatability of the quantitative data obtained from the images. Despite the numerous factors known to result in variability of SUV measured from 18 F-FDG PET/CT, the interobserver reproducibility of SUV and percentage change in SUV were higher than for measurements of CT size in a single-institution study (1).…”

“…Preliminary data from a single-institution/workstation study estimated an intraclass correlation coefficient (ICC) of 0.94 among 4 readers for determination of percentage change in SUV max (%DSUV max ) (1). We expected to observe an ICC of 0.90 resulting from greater variation across sites, given multiple readers and workstations.…”

PERCIST in Perspective

“…And simple categorization of the 18 F-FDG PET/CT study results into two groups of responders or nonresponders fails to utilize the rich data 18 F-FDG PET/CT contains. Quantitative PET assessment presented as percent change in FDG uptake would retain the inherently continuous nature of the data, and have high inter-observer reproducibility [4]. The EORTC recommendations were a great place to start standardization of PET assessment, but they did not clearly state which tumor, or tumors, to measure, and do not detail which PET parameter to utilize.…”