Influence of Staging Thoracic Computed Tomography on Radiation Therapy Planning for Esophageal Carcinoma

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Abstract
Radiation therapy with concurrent chemotherapy is frequently used as definitive treatment for esophageal carcinoma. Although thoracic computed tomography (CT) is widely used in staging esophageal carcinoma, its application to radiation therapy planning has been regarded as optional rather than mandatory. Conventional radiation therapy planning is esophagogram-based rather than CT-based. The treatment port is generated by adding 5 cm to the proximal and distal margins of the tumor-involved segment as seen on esophagogram performed in the treatment position. Historically, a maximum port length of 15 cm was recommended to avoid excessive treatment morbidity. The authors examined the limitations of such a planning protocol by projecting conventional treatment ports onto the thoracic CT of 75 consecutive newly diagnosed cases of nondisseminated esophageal squamous cell carcinoma. The authors assessed the adequacy of coverage of the primary tumor and metastatic nodes, with respect to data from thoracic CT and neck ultrasonography. It was found that up to 38% of T2-T3 tumors and 30% of short-length (≤5 cm) tumors had metastatic nodes outside the port. The addition of neck ultrasonography led to identification of an additional 5% of patients with nonpalpable nodes outside the port. It is concluded that the frequency of inadequate tumor coverage using an esophagogram-based planning protocol, with a maximum port length of 15 cm, is unacceptably high. Thoracic CT should be a mandatory rather than optional imaging investigation in guiding radiation therapy planning for esophageal cancer.