Optical coherence tomography of the esophagus in radiation therapy

Esophageal cancer is the eight most common type of cancer worldwide and the sixth leading cause of cancer-related death with a five-year survival rate of 15-25%. Prominent histopathological types of cancer are squamous cell carcinoma and adenocarcinoma. Currently, the clinical guidelines for esophageal cancer patients (>T2) involves neoadjuvant chemo-radiation therapy (nCRT) followed by esophagectomy. The main objective during radiation therapy (RT) is to precisely deliver the radiation dose to the tumor and tumor-involved lymph nodes while sparing surrounding healthy tissue. Although image-guided RT enhances the local tumor control, detailed knowledge of the tumor extent is limited and improvements are required. Computed tomography (CT) and recently magnetic resonance imaging (MRI) are the main imaging modalities used for RT planning. CT and MRI are limited in terms of resolution to visualize the tumor extent, and therefore endoscopic ultrasound (EUS) is used to assess the longitudinal extent of the tumor. However, EUS has a low soft-tissue contrast and suffers from understaging due to the limited resolution of EUS to visualize microscopic tumor extent and overstaging since it is unable to distinguish tumor infiltration from inflammatory changes. Such uncertainties require a large expansion of the gross tumor volume (GTV) into the clinical target volume (CTV) during RT planning. Optical coherence tomography (OCT) with a 10-fold higher resolution than EUS may potentially better visualize the tumor extent, which can reduce CTV margins. The aim of this thesis was to adopt OCT for image-guided RT of esophageal cancer and diagnostics of radiation-induced esophageal damages during RT of thoracic and head and neck cancer.