117 Redundant tooth loss prior to head and neck radiotherapy 5 Discussion The results of this study show that up to 61% of teeth were unnecessarily extracted at Dmax <40Gy and up to 74% at the Dmean <40Gy. To our knowledge, this is the first study to provide insight into the amount of teeth redundantly extracted prior to RT. It therefore provides arguments to drastically reduce the number of tooth extractions prior to RT for HNC. This de-escalation can help maintain the masticatory system and reduce the loss of functional units, which has a direct effect on food intake [3-9]. Not only the crushing of food, the maintenance of body weight, but also a person’s social integration is often linked to the presence of functional teeth [25]. Patients suffer not only from the underlying oncological diseases, but also from the demands of therapy. The removal of teeth is generally negatively connoted [7, 8]. The procedure itself and the expected pain can lead to a deterioration in the patient’s general situation before the start of oncological therapy. For these reasons, de-escalation in the sensitive area of the oral cavity is extremely desirable. Tumor location had a high association with unnecessarily extracted teeth. In patients with tumors located in the laryngeal, and hypopharyngeal region, only the mandibular molars and the second mandibular premolar received a dose of ≥40Gy. In these regions the primary tumor is relatively further away from the teeth. In the oral cavity, oropharynx and ‘maxillary complex’ group the number of redundantly extracted teeth was less due to the closer proximity of the primary tumor to the mandible or maxilla. This led to a higher radiation dose in the jaw bones, consistent with the delineation of GTV, CTV and PTV according to international guidelines [22]. N-state was also associated with unnecessarily extracted teeth. The presence of positive lymph nodes located near the mandible (high level II or retropharyngeal), and submandibular lymph nodes of level Ib of the neck included in the clinical (elective) target volume resulted in a higher RT dose in the mandible. In this study, a cut-off point of ≥40Gy was chosen as the threshold as indication for tooth extraction [12, 13]. Studies focusing on vascular changes at microscopic level after RT showed changes in tissue structure that occur at much lower doses [26, 27]. Studies dealing with radiation doses in typical anatomical locations of the head and neck skeleton showed average doses of 24.4 and 28.2Gy, which can be sufficient to trigger an ORN. The maximum doses measured at these specific ORN-sensitive regions were 44.3 and 48.4Gy [28, 29]. The choice of 40Gy
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