Radiotherapy planning and Molecular Imaging in Lung Cancer.

The goal of the radiotherapy (RT) planning process is to select and delineate target volumes with the best accuracy on the basis of all the available diagnostic information and the knowledge of the physiology of the disease. The recommendation of the International Atomic Energy Agency (IAEA) expert panel, is that an appropriately timed and technically adequate 2-[18F]fluoro-2-deoxy-d-glucose/Positron Emission Tomography-Computer Tomography (18F-FDG-PET/CT) imaging is an essential component in the radiotherapy treatment planning (RTP) process for lung cancer [1]. Each patient considered for radical radiotherapy should have had a staging 18F-FDG-PET/CT for RTP, acquired in treatment position and co-registered with the planning CT [2]. When used without specific adaptations for RTP, 18F-FDG-PET/CT scan can be visually correlated with the RTP CT to identify areas of disease to be included in the treatment volume. Technically the best available option is to acquire an 18F-FDG-PET/CT scan exclusively for the purpose of RTP. This scan may be performed when a staging PET has already been acquired and the patient is deemed suitable for radical radiotherapy. This approach requires two separate PET scans, which has an advantage that it removes any staging or patient selection issues but is expensive and therefore may not be possible in all health care systems because of financial or logistical limitations. Another valid approach is to acquire a single 18F-FDG-PET/CT scan in radiotherapy treatment position to serve the dual purposes of staging and target volume delineation (TVD). It is imperative that the time interval between any imaging used for the purposes of radiotherapy target volume delineation and the radiotherapy treatment delivery, should be as short as possible.