Early Detection of Lewis Lung Carcinoma Tumor Control by Irradiation Using Diffusion-Weighted and Dynamic Contrast-Enhanced MRI

Purpose:To investigate the correlation between diffusion-weighted (DW) and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) derived parameters and radioresponsiveness of Lewis lung carcinoma (LLC) tumor.Materials and Methods:LLC tumor growth in C57BL/6 mouse limb was used for the experiment. The tumors were irradiated with 10 Gy×5, or 30 Gy×2 vs. sham irradiation. Fourteen tumors were subjected to DW-MRI and DCE-MRI pre-radiotherapy and weekly imaging after radiotherapy. The temporal changes in apparent diffusion coefficient (ADC) and DCE-MRI derived parameters (K^trans, k_ep, v_e, and v_p) were correlated with tumor size, and were histologically compared with CD31 staining of resected tumors.Results:The 10 Gy×5 dose inhibited tumor growth for a week, while 30 Gy×2 controlled tumor growth for a 3-week observation period. One week after radiotherapy (week 2), irradiated tumors showed significantly higher values of ADC than untreated ones (10 Gy×5, p = 0.004; 30 Gy×2, p = 0.01). Significantly higher values of v_e were shown earlier by 30 Gy×2 vs. sham (p = 0.01) and 10 Gy×5 vs. sham irradiation (p = 0.05). Sustained higher v_e from 10 Gy×5 compared to sham irradiated tumors was evident at week 3 (p = 0.016) and week 4 (p = 0.046). A 13.8% early increase in ADC for 30 Gy×2 tumor group (p = 0.002) and a 16.5% increase for 10 Gy×5 group were noted (p = 0.01) vs. sham irradiation (which showed a 2.2% decrease). No differences were found for K^trans, k_ep, or v_p. Both radiotherapy groups demonstrated significant reduction in microvessel counts.Conclusion:Early increase in ADC and v_e correlated with tumor control by irradiation.