Applied research of a four-dimensional CT localization technique in radiotherapy and treatment planning for early lung cancer

Background: To study the feasibility of target contouring and the potential benefits to radiotherapy of four-dimensional computed tomography (4D-CT) for early stage lung cancer. Methods: We applied Brilliance CT to scan 24 lung cancer patients for 4D localization. Treatment plannings based on different breath phase CT images were designed in the Monaco 5.2 treatment planning system. Different planning was compared to find the difference of target volume, center, and dose. Results: Target volume composed of 10-breath phases (Sum) was considered as the reference volume, which was slightly larger than the volume contouring obtained by the maximum intensity projection (Mip) and extreme phase images (Exs). Target centers for Sum, Mip and Exs of CT images showed little deviation in the X, Y and Z directions. The V20 and V5 for the 4D-CT-based treatment plan showed a markedly lower dose delivered to normal tissues than those based on 3D-CT. Conclusions: For target contouring, a target contouring by 10-breath phases was superior to Mip and Exs. As the gross target volume (GTV) contouring obtained by the maximum intensity projection and extreme phase were similar to that of the reference target, they can support the contouring target and reduce the time and work. Treatment plan comparisons indicated that normal lung tissues received a remarkably lower dose when a 4D-CT-based plan was used.