223 General discussion 7 In the 358 patients included in Chapter 5, 1759 teeth were extracted of which 1274 teeth (74%) appeared to have been removed redundantly, based on the mean dose (Dmean) of <40Gy. Using the maximum dose (Dmax) of <40Gy, 1080 teeth (61%) appeared to have been removed redundantly. Of the potential factors contributing to teeth receiving a cumulative RT dose ≥40Gy, tumor location and N-classification emerged as the most important factors in the multivariable regression analysis. The patients with OPSCC in Chapter 6 who underwent tooth extraction(s) prior to IMRT were more likely to experience significant weight loss of more than 5% during CRT/BRT. The number of teeth extracted and the number of functional units lost did not influence the degree of weight loss and the need for tubefeeding (TF). These results provided arguments to drastically reduce the need and number of tooth extractions prior to RT for HNC. Accuracy of tooth removal Cut-off point In this study, a cut-off RT dose of ≥40Gy was chosen as the threshold as indication for tooth extraction [20, 91]. The choice of 40Gy as the threshold dose for the risk of developing ORN as described in the Dutch National Protocol is empirical [20, 91]. Vascular changes in tissue structure after RT occur at much lower doses [93, 94] and average doses of 24.4 and 28.2Gy corresponding with maximum doses of 44.3 and 48.4Gy have been shown sufficient to trigger an ORN [95, 96]. Several other studies suggest using 50Gy or 60Gy for the mandible or even 70Gy for the maxilla as a reference value for the development of ORN [95-99], with only one Delphi study discussing a critical radiation threshold for prophylactic removal of teeth [100]. Further research is needed before the Dutch guidelines that aim to minimize this risk as much as possible are amended. Thereby, it is important that it is clearly described whether the mean or the maximum dose must be used. Dose-distribution There are previous publications describing radiation doses to portions of the mandible and maxilla [22, 101-104], whereby reporting the doses in ipsi- and contralateral is very crucial. This was clearly illustrated by our results for tumors in the “parotid region” where only the mandibular molars and second mandibular premolar on the ipsilateral side received a dose ≥40Gy. While some studies looked at RT dose in terms of a volume percentage of the jaw [103], others outlined the teeth individually [22, 101, 102] or used a cylinder [104], like our study. We drew one
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