A comparative study of the target volume definition in radiotherapy with «Slow CT Scan» vs. 4D PET/CT Scan in early stages non-small cell lung cancer.

Objectives: To evaluate the use of 4D PET/CT to quantify tumor respiratory motion compared to the «Slow»-CT (CTs) in the radiotherapy planning process.

Material And Methods: A total of 25 patients with inoperable early stage non small cell lung cancer (NSCLC) were included in the study. Each patient was imaged with a CTs (4s/slice) and 4D PET/CT. The adequacy of each technique for respiratory motion capture was evaluated using the volume definition for each of the following: Internal target volume (ITV) 4D and ITVslow in relation with the volume defined by the encompassing volume of 4D PET/CT and CTs (ITVtotal). The maximum distance between the edges of the volume defined by each technique to that of the total volume was measured in orthogonal beam's eye view.

Results: The ITV4D showed less differences in relation with the ITVtotal in both the cranio-caudal and the antero-posterior axis compared to the ITVslow. The maximum differences were 0.36mm in 4D PET/CTand 0.57mm in CTs in the antero-posterior axis. 4D PET/CT resulted in the definition of more accurate (ITV4D/ITVtotal 0.78 vs. ITVs/ITVtotal 0.63), and larger ITVs (19.9 cc vs. 16.3 cc) than those obtained with CTs.

Conclusion: Planning with 4D PET/CT in comparison with CTs, allows incorporating tumor respiratory motion and improving planning radiotherapy of patients in early stages of lung cancer.