Introduction: Lung cancer has the highest mortality rate of any cancer in the world. One type of treatment for lung cancer is radiotherapy. Greater accuracy of radiotherapy treatment is ensured by daily image verification of the patient's position before treatment. Cone beam computed tomography is a method of image verification in which a three-dimensional image of a patient is compared to a three-dimensional image obtained on a computed tomography Simulator. Cone beam computed tomography allows the registration process to focus on bone tissues or on soft tissues. Purpose: The purpose of the master's thesis is to determine if there are any differences between the spine registration or the registration on the carina of the trachea in respect to tumour registration. And in which direction it differs the most. In addition, we want to determine, whether the location of the tumour and the number of affected lymph node regions have an impact on registration differences. Methods: The study included 40 patients with lung cancer, whose position was verified with cone beam computed tomography prior to radical radiotherapy. We used 4 verification images of each patient before the 1st, 10th, 15th and 20th radiotherapy fraction and performed registration on the tumour, on the spine and on the carina of the trachea. Differences were recorded in the vertical, longitudinal, and lateral directions. Results: Differences between tumour-spine registration and tumour-carina of the trachea registration are the greatest in the longitudinal direction. Between the tumour registration and the spine registration there is an average difference of 2.5 mm in longitudinal direction and between the tumour registration and the registration on the carina of the trachea the average difference is 1.7 mm. Registration on the carina of the trachea is more accurate than spine registration for centrally located tumours in all directions. The same is observed in peripheral tumours, except in the vertical direction. Additionally, registration on the carina of the trachea is better on all days of measurement and in all directions at the N3 stage of the disease. Due to the appearance of major anatomical changes during therapy, 3 patients required re-preparation for irradiation. Discussion and Conclusion: The results show that registration on the carina of the trachea is more reminiscent of tumour registration than spinal registration. Because image registration on the carina of the trachea is only possible with three-dimensional verification, cone-beam computed tomography is preferred method for image verification in lung cancer radiotherapy. In addition to providing with greater accuracy, it also allows to track anatomical changes that may occur during irradiation.
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