Computed tomography (CT) images, used for radiotherapy planning, are often caught out in lung target volumes delineation because of their inability to differentiate between neoplasia, inflammation and atelectasia. Positron Emission Tomography (PET) is a new functional imaging modality and is currently used in the diagnosis and the staging of lung cancers. The aim of this study is to evaluate the impact of 4D 18F-FDG-PET-CT on radiotherapy planning for lung cancers.

Many PET studies have been interested in lung radiotherapy volumes definition, however lacking any standardisation. Effectively, the use of PET images is difficult because of the poor image quality resulting from noise and partial volume effects induced blurring. Moreover, due to the long duration of PET acquisitions, respiratory motions are inevitable and result in artifacts in the PET images affecting the volumes and contrast of the tumour: tumours may appear larger while their activity can be lower. To overcome these limitations, we propose to use a 4D PET-CT, ie a PET-CT acquisition system synchronized with respiration in order to compare CT-simulation target volumes and PET target volumes after application of different approaches for partial volume effect correction, respiratory motion correction and automatic segmentation method of functional volumes. For this purpose, patients with a non small cell lung cancer and having to be treated with radiotherapy or radio-chemotherapy underwent CT-simulation and 4D PET-CT in radiotherapy treatment position. The target volumes and the dosimetries obtained with both modalities were compared.

Inclusion Criteria:

• age ≥ 18 years old
• patients with unresectable non small cell lung cancer having to be treated with radiotherapy or radio-chemotherapy

Exclusion Criteria:

• neo-adjuvant treatment
• patient treated previously with thoracic radiation
• patient unable to support 4D PET-CT
• pregnant or breast-feeding woman