PT - JOURNAL ARTICLE
AU - Rahmim, Arman
AU - Schmidtlein, C.
AU - Bak-Fredslund, Kirstine
AU - Subramaniam, Rathan
AU - Morsing, Anni
AU - Keiding, Susanne
AU - Munk, Ole
TI - Application of novel PET metric to quantify liver metastases for enhanced prognostication of clinical outcome
DP - 2016 May 01
TA - Journal of Nuclear Medicine
PG - 352--352
VI - 57
IP - supplement 2
4099 - http://jnm.snmjournals.org/content/57/supplement_2/352.short
4100 - http://jnm.snmjournals.org/content/57/supplement_2/352.full
SO - J Nucl Med2016 May 01; 57
AB - 352Objectives We investigated application of a novel quantitative metric, enabling placement of unequal emphases on PET tumor uptake vs. volume information, to assess prognostic value in patients with intrahepatic colorectal metastases.Methods The metric, denoted generalized effective total uptake (gETU), is derived by analogy to a model of generalized effective uniform dose (gEUD) as used in radiation therapy. It is formulated as gETU(a)= ( Δv [asterisk] Σiuia )1/a for a given tumor (or collection thereof) with N voxels each of volume Δv and PET uptake ui (i=1&#8943;N). The proposed metric has the attractive feature that it generalizes commonly utilized metrics using a single additional degree-of-freedom or parameter ‘a’. Specifically, values of a=0, 1 and ∞ correspond to MTV, TLG and SUVmax, respectively. We applied this metric to n=50 patients with intrahepatic-only colorectal metastases imaged at baseline with FDG PET/CT (60min post-injection, 3min/bed, Siemens Biograph). Tumors were segmented from PET images using (i) 50% background-corrected SUVmax, (2) SUV>2.5, and (3) SUV>3.0 thresholding (Hermes Hybrid Viewer PDR). Five conventional metrics were considered for comparison against the proposed gETU metric, namely MTV, TLG, SUVmax, SUVmean and SUVpeak. Kaplan-Meier survival analysis of overall survival (OS) was performed, where, for a given metric, the subjects were subdivided into two groups using the median threshold. Following this, the hazard ratios (HR) between the higher percentile to the lower percentile groups were computed using Cox proportional hazards regression. The proposed gETU metric was generated for a range of exponents a (in logarithmic increments of 0.1), and subsequently optimized.Results Aside from PET-based analysis, predictive factors considered were number of metastatic tumors, age and sex, for which Cox proportional hazards regression revealed no significance for OS prediction (p-values=0.23, 0.92 and 0.82, respectively). As such, the rest of the analysis included only PET-based metrics. SUV>3.0 segmentation resulted in generally improved prediction performance for the various metrics, and our gETU metric was optimized for a=7.9, i.e. when greater emphasis is put on PET uptake than volume. This is unlike TLG (a=1), which places equal emphasis on volume and uptake, and unlike MTV or SUV, which neglect either uptake or volume, respectively. The optimized HR values for MTV, TLG, SUVmax, SUVmean, SUVpeak and gETU were 2.84, 2.80, 1.19, 1.93, 1.88 and 3.30, respectively, while the p-values for curve separation (i.e. ability to reject the null hypothesis that HR=1) were 0.0055, 0.0063, 0.62, 0.068, 0.80 and 0.0018, respectively. MTV/TLG and SUVmax/mean/peak were outside the 85% and 99% confidence intervals of gETU, which depicted greatest outcome prediction performance.Conclusions The proposed framework, enabling placement of unequal emphases on PET tumor uptake vs. volume information, resulted in enhanced clinical outcome prediction for patients with intrahepatic colorectal metastasis.