Use Of Pet In Radiationtreatment Planning For Thoracic Malingnancies

Radiotherapy has a crucial role in the treatment strategy for patients with tumor localized in the thorax. Accurate diagnosis and staging of the cancer is essential for precise administration of curative intent using radiation therapy. The main objective of radiotherapy is to achieve improved local control with dose escalation to the tumor while decreasing the probability of side effects by reducing radiation exposure to healthy surrounding organs. Computed tomography (CT) is generally the primary modality for image-based treatment planning, but conventional anatomic imaging with CT has limited sensitivity in distinctly identifying the anatomic borders of the tumor. The radiation oncologists still manually contour the tumor using CT images, and this component is significantly related with inter-observer and intra-observer contouring variability. Precise and accurate localization of radiotherapy targeted to the tumor is critical for optimizing the therapeutic ratio by limiting the amount of normal tissues receiving radiation, maximizing coverage of tumor volumes, and limiting geometric miss of tumor using advanced radiotherapy techniques. A new imaging technique has therefore been sought to allow precise delineation of the cancer target to be irradiated. F18 fluorodeoxyglucose positron emission tomography/computed tomography (F18 FDG PET/CT) has been reported as a reliable method for staging and detection of tumor that is located at thorax such as lung or esophageal tumors. Because F18 FDG PET/CT provides biological information of tumor in addition to anatomical information, it significantly decreases intraobserver variability in terms of target delineation. For instance, it decreases the sizes of tumors and accurate definition of the involved lymph nodes by separating tumor tissue from atelectasis area and identifying lymph nodes, whose sizes are increased because of benign, therefore provides precise radiotherapy. The accurate delineation of the tumor using F18 FDG PET/CT allows dose escalation for lung cancer treatment while minimizing any side effects. Furthermore, it can help in treatment planning by deciding the treatment volume by detecting lymph nodes and distant metastatic area which cannot be identified by other imaging modalities for esophageal cancer. In this study, the contribution of F18 FDG PET/ CT to the radiotherapy planning process for cancer located in the thorax was evaluated.