SUR for mediastinal metastatic lymph node status in non-small-cell lung cancer patients
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LETTER TO THE EDITOR
SUR for mediastinal metastatic lymph node status in non-small-cell lung cancer patients Eric Laffon 1,2,3,4
&
Roger Marthan 1,2,3
Received: 4 May 2020 / Accepted: 18 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Dear Sir, In a recent exploratory study using 18F-FDG PET imaging, Yang et al. performed Patlak’s graphical analysis (PGA) in primary tumor (PT) and mediastinal metastatic lymph nodes (MLN) of non-small-cell lung cancer (NSCLC) patients. Presence or absence of distant metastases discriminated group M1 and group M0, respectively [1]. For MLN, in contrast to the standard uptake value (SUV), only the PGA uptake-rate constant (Ki) was significantly higher in M1 than in M0, whereas for PT, both Ki and SUV were significantly higher in M1 than in M0. The authors concluded that Ki obtained from PGA may become an important tool for earlier, noninvasively, identifying MLNs in NSCLC patients. However, Yang et al. commented that, unlike SUV that only requires a static acquisition (usually) starting at 60 min post-injection, PGA Ki is rarely assessed, in clinical routine, owing to a time-consuming dynamic PET acquisition that is achieved for 60 min after bolus injection of the tracer. Moreover, PGA is based on an input function (at least image-derived, as in the current study) and a tissue timeactivity curve that can be obtained from volumes of interest (VOIs) manually drawn over early frames and then projected onto all frames. Then, PGA plots tissue/blood activityconcentration ratio versus so-called stretched time (i.e., ts) and, subsequently, chooses the “best ts” for performing a This article is part of the Topical Collection on Oncology - Chest * Eric Laffon [email protected] 1
CHU de Bordeaux, F-33000 Bordeaux, France
2
Centre de Recherche Cardio-Thoracique de Bordeaux, University Bordeaux, F-33000 Bordeaux, France
3
INSERM U-1045, Centre de Recherche Cardio-Thoracique de Bordeaux, F-33000 Bordeaux, France
4
Service de Médecine Nucléaire, Hôpital du Haut-Lévèque, Avenue de Magellan, 33604 Pessac, France
linear data fitting whose slope is Ki. Finally, and most importantly, in the currently available PET systems, PGA is restricted to one bed position covering the region of interest, here, the patient’s chest, and, hence, an additional static PET acquisition over the whole body is needed at 60 min post-injection for identifying distant metastases. Nevertheless, we still believe that the PGA-Ki results for MLN obtained by Yang et al. from dynamic PET imaging are of great interest because the reported Ki efficiency may actually be adapted to static PET imaging performed in clinical routine. Indeed, van den Hoff et al. have clearly shown, in 18 F-FDG PET imaging, that the tumor-to-blood standard uptake ratio (SUR = SUVtumor/SUVblood) is a relevant surrogate for Ki, under the (PGA) condition of irreversible trapping [2]. Since then, many articles related to other tracers than 18F-FDG and targeting different tissues have further shown that this ratio, called or
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