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From RECIST to PERCIST: Evolving Considerations for PET Response Criteria in Solid Tumors

¹ Division of Nuclear Medicine, Department of Radiology, Johns Hopkins University School of Medicine, Baltimore, Maryland; and ² Department of Oncology, Johns Hopkins University School of Medicine, Baltimore, Maryland

View larger version (33K): [in this window] [in a new window]   FIGURE 1.  Kinetics of tumor cell kill and relation to PET. Line A represents brisk tumor response that would produce cure after only 4 cycles of chemotherapy. Line B represents minimum rate of tumor cell kill that will lead to cure in 6 cycles of treatment. Both lines would be associated with negative PET scan after 2 cycles of chemotherapy. In contrast, line C represents rate of tumor cell kill that would be associated with negative PET scan after 4–6 cycles but would not produce cure. Importantly, PET scan for line C would likely be positive after 3 cycles (27).

View larger version (14K): [in this window] [in a new window]   FIGURE 2.  Number of papers that included use of tumor ROIs, as function of year of publication. Papers were identified by Medline search that queried for FDG AND SUV OR "standard uptake value" OR "standardized uptake value" OR "standardised uptake value"). Only human 18F-FDG oncology studies were included. ROI max refers to maximal pixel in tumor. ROI peak refers to small (typically 15 x 15 mm) fixed-size ROI centered on most metabolically active part of tumor. ROI isocontour refers to irregular ROI defined by isocontour set at, for example, some percentage of maximal pixel. ROI manual refers to manually drawn ROI. Only a subset of these papers describes response assessment studies.

View larger version (35K): [in this window] [in a new window]   FIGURE 3.  Example calculation of liver background for normalization of SUL. Images are displayed from Advantage Workstation (GE Healthcare). A 3-cm-diameter 3-dimensional ROI (ROI 1) is placed on normal inferior right lobe of liver (arrowhead). Average SUL and SD in ROI are displayed (arrows). Liver background is calculated as follows: (1.5 x average SUL liver) + (2 x SD average SUL liver). For this example, (1.5 x 1.4) + (2 x 0.2) = 2.5. Therefore, tumor SUL peak should be >2.5 in order to apply PERCIST criteria for this example.

View larger version (70K): [in this window] [in a new window]   FIGURE 4.  PET/CT images obtained before (1) and after (2) treatment of pancreatic carcinoma with experimental therapy targeting mammalian target of rapamycin. Note profound decline in SUL (41%) despite stable pancreatic mass anatomically (arrows). This decline represents metabolic partial response by PERCIST (41% decline in marker lesion at 2 wk after therapy). Not all metabolic PMRs are clinically relevant; relevance will depend on the specific treatment.

View larger version (67K): [in this window] [in a new window]   FIGURE 5.  PET/CT image obtained before (1) and after (2) treatment of pancreatic carcinoma with experimental therapy targeting mammalian target of rapamycin. Glycolysis and apparent necrosis are profoundly reduced in intensely 18F-FDG–avid liver metastases. Although a reduction of more than 50% in SUL peak would suggest partial metabolic response, new lesion indicative of progressive metabolic disease is evident in left retroperitoneum (arrow).

View larger version (35K): [in this window] [in a new window]   FIGURE 6.  (A) Patient with extensive non-Hodgkin lymphoma before treatment. Tumor with most intense 18F-FDG activity is in abdomen. Transverse images of easily measurable right axillary lymph node on CT are shown for convenience. (B) Commercial software tool (PET Volume Computed Assisted Reading; GE Healthcare) was used to localize foci of 18F-FDG uptake greater than mean liver SUL + 2 SDs of normal liver background (red). Manual intervention is required to separate normal 18F-FDG–avid foci, including brain, heart, and excreted urine, from relevant tumor. This semiautomated segmentation can be used to estimate total lesion glycolysis.