Diffusion weighted imaging-based tumor growth rate for predicting long-term survival in nasopharyngeal carcinoma

To explore the prognostic value of tumor special growth rate (TSGR) in patients with NPC and investigate the potential of diffusion-weighted imaging (DWI) habitat analysis as a surrogate marker.

Patients who underwent two MRI scans before any type of treatment at two institutes were included. Radiologists manually delineated the volume of the primary tumor, and the doubling time and TSGR were calculated. Correlation between TSGR and long-term survival was evaluated using multivariate Cox analysis. Moreover, a radiologist delineated the tumor on b = 0 s/mm² images during the first MRI scan. Each tumor was divided into two subregions based on the individual mean apparent diffusion coefficient value (ADC_Mean), and the ADC value (ADC_down [mm²/s] and ADC_up [mm²/s]) of each subregion was calculated. ADC values for diagnosing TSGR and predicting survival were evaluated and validated using 5-fold cross-validation (iterations = 1000) and in an independent cohort.

A total of 98 patients were included (median age: 51 years; 24 females; training cohort: 64). The median doubling time was 131.9 days. Patients in the rapid-growth group (TSGR ≥ 1.4%) had significantly poorer survival than those in the slow-growth group (TSGR < 1.4%) in both the training and validation cohorts (p ≤ 0.006). ADC_down was a valuable factor in predicting TSGR (area under the curve: 0.792). Notably, the addition of ADC_down further improved the predictive value of TNM stage (0.663-0.848 vs. 0.631-0.785).

Patients with high ADC_down value may have the rapid-growth potential and were more likely to have a poor prognosis.