Changes of tumor size and tumor contrast enhancement during radiotherapy for non-small-cell lung cancer may be suggestive of treatment response.

We evaluated sequential dynamic contrast-enhanced CT (DCE-CT) scans to assess the possibility of early prediction of treatment responses by quantifying the tumor size reduction and the change in tumor enhancement during and after a course of radiotherapy (RT). Thirty-nine patients with non-small-cell lung cancer were treated with RT for initial treatment. DCE-CT scan was performed within one week before the beginning of treatment, after 17 or 18 fractions (34 or 36 Gy), and 1 week and 1 month after the end of RT. The correlation between the relative decrease in tumor diameter and that in the attenuation value was evaluated. Nineteen patients were evaluated in this study. The median tumor size was 39.5 mm at the start of treatment, 30.8 mm at 34-36 Gy, and 16.1 mm 1 month after the end of RT. The relative decrease in tumor diameter at 34-36 Gy well correlated with that 1 month after treatment (r = 0.85, r: Pearson's correlation coefficient, p < 0.001). Relative change in the attenuation value at the rim of the tumor at 34-36 Gy did not significantly correlate with the change in tumor diameter 1 month after the completion of RT, but in the center of the tumor, the change of the attenuation value in the delayed phase correlated with the change in tumor diameter. The decrease of tumor diameter during RT may be predictive of treatment response. The relative change of tumor enhancement in the center of the tumor in the delayed phase correlated with tumor shrinkage 1 month after the completion of RT.