ESTRO 2021 Abstract Book

S828

ESTRO 2021

events more than Grade 2 equal to 24% (n=11) in the acute and 4% (n=2) in the late toxicity. During RT course five patients out of 46 needed a nutritional support with feeding tube placement, while the majority had Grade 1 weight loss. Considering the remaining acute G3 events, they were dysphagia (4 cases), mucositis (2 cases) and cutaneous toxicity (1 case). Moreover, clinical outcomes of the MB were compared with those obtained in a retrospective cohort of 17 pts with LANPC treated with only IMRT. In this group, after a median follow-up of 51 months, LC was 81%, 3-year LRFS and DMFS were 85% and 81%, respectively. Conclusion Results showed excellent outcome and acceptable radiation-related side effects in patients treated with a MB approach. Our results are also strengthened by the comparison with the historical group treated with IMRT only. A longer follow-up is required to confirm these promising preliminary results. PO-0996 Dose guided surgery and its impact on the surgical management of mandibular osteoradionecrosis N. West 1 , N. Willis 1 , J. Adams 2 , M. Kennedy 2 , G. Jenkins 2 , M.S. Iqbal 1 , Z. Davidson 1 1 Newcastle upon Tyne Hospitals Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom; 2 Newcastle upon Tyne Hospitals Trust, Surgery, Newcastle upon Tyne, United Kingdom Purpose or Objective Following radiotherapy for head and neck cancer, a cohort of patients present with mandibular osteoradionecrosis (ORN). The reported incidence of ORN varies greatly between 4.7% to 37.5%, presenting between 6 and 36 months post irradiation. Onset is initiated by trauma or infection (from tooth extraction, surgery, biopsy, denture irritation, accidents or infection) to the local area and predominantly focussed in the mandible. There is strong evidence suggesting a trend between doses greater than 50Gy and the onset of ORN exists, with areas exposed to doses lower than 50Gy reported to be at significantly lower risk of ORN. Local practice is dose guided surgery; propagating and visualising delivered radiotherapy dose to assist the 3D surgical planning process; informing surgeons about areas of mandible that received high dose to guide resection and displaying areas that received low doses of radiotherapy to assist in locating fixation devices. Prior to the implementation of dose guided surgery, clinical and radiological assessment was used to guide the surgical design. Here we investigate how dose guided surgery has changed surgical designs. Materials and Methods We retrospectively analysed 12 patients who underwent 3D surgical planning for mandibular ORN. The surgical plans, in particular the resected volumes of mandible and the location of fixation devices, were compared to the dose guided surgery approach; superimposed delivered radiotherapy dose on a radiologically reconstructed mandible to guide surgery. Results We found significant differences between the surgery received and surgical plan as indicated by the dose guided surgery approach, with resection volumes being clinically different. Notably when considering the 3D delivered dose, it is evident that clinical and radiological assessment alone risks placing cut planes and fixation devices in areas that had high radiotherapy doses and at high risk of ORN (>50Gy). In one of these instances a cut plane received >65Gy. This patient represented after surgery with ORN in the vicinity of the cut plane and screw locations (figure 1).

Conclusion As ORN can manifest as a progressive disease, radiological and clinical assessments alone are not sufficient in guiding the surgical management of osteonecrotic mandible following radiotherapy. Without knowledge of delivered radiotherapy dose there is an increased risk of surgical failure and with patients representing after this high cost and high burden procedure. Dose guided surgery should become a standard of care for this cohort of patients.