Variation in background intensity affects PET-based gross tumor volume delineation in non-small-cell lung cancer: the need for individualized information

Prognostic value of metabolic tumour volume on baseline 18F-FDG PET/CT in addition to NCCN-IPI in patients with diffuse large B-cell lymphoma: further stratification of the group with a high-risk NCCN-IPI

PURPOSE

The purpose of this study was to determine the prognostic value of metabolic volumetric parameters as a quantitative index on pre-treatment ¹⁸F-FDG PET/CT in addition to the National Comprehensive Cancer Network International Prognostic Index (NCCN-IPI) in patients with diffuse large B-cell lymphoma (DLBCL).

METHODS

A total of 103 consecutive patients with DLBCL and baseline FDG PET/CT were retrospectively evaluated. Quantitative metabolic parameters, including total metabolic tumour volume (TMTV) using a standardized uptake value (SUV) of ≥2.5 as the threshold, were estimated. Receiver operating characteristic curve analysis was used to determine the optimal cut-off values for the metabolic parameters. The relationships between study variables and patient survival were tested using Cox regression analysis. Patient survival rates were derived from Kaplan-Meier curves and compared using the log-rank test.

RESULTS

Median follow-up was 34 months. In patients with a low TMTV (<249 cm³), the 3-year progression free survival (PFS) rate was 83% and the overall survival (OS) rate was 92%, in contrast to 41% and 57%, respectively, in those with a high TMTV (≥249 cm³). In univariate analysis, a high TMTV and NCCN-IPI ≥4 were associated with inferior PFS and OS (P < 0.0001 for all), as was a high total lesion glycolysis (P = 0.004 and P = 0.005, respectively). In multivariate analysis, TMTV and NCCN-IPI were independent predictors of PFS (hazard ratio, HR, 3.11, 95% confidence interval, CI, 1.37-7.07, P = 0.007, and HR 3.42, 95% CI 1.36-8.59, P = 0.009, respectively) and OS (HR 3.41, 95% CI 1.24-9.38, P = 0.017, and HR 5.06, 95% CI 1.46-17.60, P = 0.014, respectively). TMTV was able to separate patients with a high-risk NCCN-IPI of ≥4 (n = 62) into two groups with significantly different outcomes; patients with low TMTV (n = 16) had a 3-year PFS rate of 75% and an OS rate of 88%, while those with a high TMTV had a 3-year PFS rate of 32% and an OS rate of 47% (χ² = 7.92, P = 0.005, and χ² = 8.26, P = 0.004, respectively). However, regardless of TMTV, patients with a low-risk NCCN-IPI of <4 (n = 41) had excellent outcomes (3-year PFS and OS rates of 85% and 95%, respectively).

CONCLUSION

Pretreatment TMTV was an independent predictor of survival in patients with DLBCL. Importantly, TMTV had an additive prognostic value in patients with a high-risk NCCN-IPI. Thus, the combination of baseline TMTV with NCCN-IPI may improve the prognostication and may be helpful guide the decision for intensive therapy and clinical trials, especially in DLBCL patients with a high-risk NCCN-IPI.

Current Methods to Define Metabolic Tumor Volume in Positron Emission Tomography: Which One is Better?

Numerous methods to segment tumors using ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG PET) have been introduced. Metabolic tumor volume (MTV) refers to the metabolically active volume of the tumor segmented using FDG PET, and has been shown to be useful in predicting patient outcome and in assessing treatment response. Also, tumor segmentation using FDG PET has useful applications in radiotherapy treatment planning. Despite extensive research on MTV showing promising results, MTV is not used in standard clinical practice yet, mainly because there is no consensus on the optimal method to segment tumors in FDG PET images. In this review, we discuss currently available methods to measure MTV using FDG PET, and assess the advantages and disadvantages of the methods.