224 Chapter 7 cylinder per tooth over the full length of the jaw, while Alberga et al. used a 6 mm high cylinder at standardized locations in the jaw [104]. These different methods for determining RT doses to jaw areas limit the ability to compare these studies. Tumor location had a high association with dose-distribution and thus 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 gross tumor volume (GTV), clinical target volume (CTV) and planning target volume PTV according to international guidelines [105]. N-state, describing the spread of cancer to nearby lymph nodes, 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. Further research, preferably in a multicenter setting, is needed to extrapolate our results to other treatment centers, as local experience aspects of treatment planning and normal tissue sparing differ. With the introduction of IMPT further dose-sparing effect on the dentition, especially for tumors located further away from the tooth-bearing regions, seems likely but single radiation dosages exceeding 40Gy still exist [104]. Therefore, in addition to properly assessing the tumor location and the location of the positive lymph nodes, good consultation with the radiation-oncologist remains of great clinical importance. The development of artificial intelligence may contribute in the estimation of expected RT doses in the head and neck to make dental assessment more predictable [106, 107]. Possible consequences of tooth removal Our study in Chapter 6 suggests that tooth extractions contribute to significant weight loss during treatment, but a reduced number of functional units was not associated with weight loss of more than 5 percent. The latter may be due to the relatively high number of edentulous patients in our cohort who were able to undergo extractions (e.g., root tips or impacted wisdom teeth), but whose number of functional units could not decrease any further.
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