Imaging for Target Volume Definition and Response Assessment in Lung Cancer.

Target volume definition is of obvious importance in successful radiotherapy. Single-energy CT scans remain the standard, but FDG-PET-CT scans aid the determination of which lymph nodes should be included in the gross tumor volume and to fine-tune areas of cancer involvement. FDG-PET-CT imaging remains the gold standard in clinical practice. Hypoxia and proliferation tracers are still investigational, as is PET-guided redistribution of the radiation dose within the tumor. Contrast-enhanced CT as well as 4D CT scans contain information such as the characteristics of the lungs that are related to individual radiosensitivity, ventilation, and perfusion. Dual-energy CT imaging holds promise for the future for characterization of both tumor and normal tissues. The assessment of response after radiotherapy on the basis of CT scans remains difficult because of inflammatory and fibrotic changes. RECIST is still the standard. FDG avidity suffers from too high rates of false positive and false negative signals and is therefore not recommended, except on clinical indication.