Correlation of standard uptake value (SUV) and tumor to blood standard uptake ratio (SUR) with the metabolic uptake rate derived from quantitative dual time point measurements.

Aim:

The standard uptake value (SUV) is widely used for quantitative assessment of tumor metabolism in FDG-PET. However, the SUV approach has well known limitations. Recently, we have shown that SUR overcomes most of these limitations [1,2]. Excellent linear correlation of SUR and Km from Patlak analysis was found using dynamic imaging of liver metastases. However, due to the perfectly standardized uptake period used for SUR determination and the comparatively short uptake period these results are not directly applicable to clinical whole body examinations, in which the uptake periods often vary considerably. Therefore, the aim of this work was to investigate the correlation of SUR and Km in clinical whole body scans, where Km was approximated by Ks derived from dual time point (DTP) measurements [3].

Methods:

DTP FDG-PET/CT was performed in 89 consecutive patients with histologically proven NSCLC. In the PET images the primary tumor was delineated with an adaptive threshold method. For determination of the blood SUV the aorta was delineated manually in the attenuation CT. SUR values were computed as ratio of tumor SUV and blood SUV. SUR values were scan-time-corrected to 60 min p.i. as described in [2]. Metabolic uptake rate Ks was computed similar to the procedure in [3]. The correlation of SUV and SUR with Ks was investigated. The prognostic value of SUV, SUR and Ks for and overall survival (OS) progression free survival (PFS) was investigated with univariate Cox regression in a homogeneous subgroup (N=31).

Results:

There was highly significant correlation of SUR and Ks (R2=0.93). However, the correlation coefficient appeared somewhat lower than previous results obtained from dynamic imaging and standardized uptake times (R2=0.96 [1]). As expected, SUV showed markedly lower correlation with Ks than SUR (R2=0.68). In the survival analysis none of the investigated parameters were prognostic for OS. Univariate Cox regression revealed SUR and Ks as prognostic factors for PFS.

Conclusion:

Our results show that in clinical whole body PET the correlation of uptake values with the metabolic trapping rate can be improved notably by blood normalization and scan-time-correction. Furthermore, the high correlation of SUR with Ks indicates that for histologically unambigous tumor lesions DTP does not provide added value in comparison to SUR.

Literature:

[1] EJNMMI Res 2013,3:77
[2] EJNMMI Res 2014,4:18
[3] EJNMMI Res 2012,3:16