Page 116 - 18F-FDG PET as biomarker in aggressive lymphoma; technical and clinical validation

Chapter 5
to be completed, which was not included in the time per patient reported in Ilyas study. Yet, also in our study, we found that when total metabolic tumor volume was derived using the preselection and when unwanted normal tissue uptake could be removed and missed lesions could be added by single mouse clicks, the overall processing time was typically less than 5 min. In cases where manual corrections or manual definitions of the VOIs were needed, processing time could well exceed 20 min.
Another important finding in the Ilyas study and our study is that the SUV≥2.5 method showed the highest interobserver reliability. Interestingly though, the observers in our study considered that SUV≥2.5 often overestimated the volume compared with other methods and was almost never chosen as their preferred method on a patient-level.
However, a recent study (partly by the same authors) showed that a slightly higher threshold (SUV≥4.0)outperformed the SUV≥2.5 in terms of success rate [23].
A recent phantom and patient study in primary mediastinal B cell lymphoma that compared four different MTV methods found that SUV≥2.5 resulted in an overestimation, particularly at high SUV values and 41%MAX underestimated MTV when there were high levels of heterogeneity [24].
In a publication by Meignan et al. [12], two observers used two percentage-based methods for MTV assessment in DLBCL (41%MAX and a variable SUVmax threshold that visually resulted in optimal segmentations). They found substantial reliability of 0.99 for the 41%MAX threshold and poor reliability of 0.86 for the variable percentage of SUVmax according to Lin’s concordance correlation coefficient. This study also suggests that reliability decreased with an increasing level of user interaction.
Based on the ratings of individual lesions it could be argued that no single semi- automated segmentation method performed well for every patient and within every lesion of that patient. Lymphoma sites can be difficult to segment because of heterogeneity within and between lesions. Some patients have many lesions, making it almost impossible to delineate each lesion. Besides that, it should be noted that a visual check of the generated segmentation by an experienced nuclear
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