ABSTRACT
Magnetic resonance imaging (MRI) provides superior soft tissue contrast as compared to other imaging modalities. The treatment planning computed tomography (CT) can be fused with the MRI to better delineate the gross tumor volume as well as any lymph nodes detected. MRI is a useful tool when determining the gross tumor volume (GTV) as well as the extent of tumor invasion into soft tissues. The GTV represents the visible extent of the malignant tumor. In the case of lung cancer, it is constituted by the primary lesions and clinically involved lymph nodes as well as any metastatic disease that is included in the treatment plan. In addition to being a powerful diagnostic tool, positron emission tomography (PET)-CT also has a positive impact on radiation treatment planning. The utilization of PET-CT information during radiation treatment planning leads to decreased inter-observer contouring variability. PET-CT may overestimate the lymph node (LN) involvement and, whenever possible, LN involvement should be pathologically confirmed.
