Clinical target volume definition in laryngeal and hypopharyngeal cancer

In head-and-neck radiotherapy, including larynx and hypopharynx regions, accurate determination of the tumor extent is important. On one side, a recurrence of the tumor might occur, when the extent of the tumor is underestimated, whereas, on the other hand, overestimation of the tumor extent might result negative side-effects for the patient. Determining the extent of the tumor on clinical images is not easy, as not all tumor tissue is recognizable as such. In this thesis, however, the extent of the tumor was accurately determined based on histopathological sections. The histopathological sections where acquired after excision of the larynx and/or hypopharynx. The extent of the tumor was determined by a pathologist delineating the tumor extent. After 3D-reconstruction of the delineated tumor volume determined on the histopathological sections, this reconstructed tumor volume was compared with the tumor volume visible on clinical images of the patient, acquired using either CT, MRI or FDG-PET. Based on this comparison, we could determine which safety margin around the clinically visible tumor volume was needed to include the part of the tumor invisible on clinical images. The various imaging techniques (CT, MRI and PET) required each their own safety margin. For PET images, the delineation of the tumor was automated with various methods, which methods also required their own safety margins. Adaptation of the safety margin for inclusion of the invisible tumor extent on clinical imaging, is of great importance to obtain an accurate definition of the tumor extent.