ESTRO 2021 Abstract Book

S286

ESTRO 2021

median Dmax and median D2%. However, both metrics were higher in ORN cases with respect to control cases by a similar amount (ratios of 1.013 and 1.011, respectively). Conclusion Our results suggest that the mandible should be considered a serial-parallel organ as ORN incidence is related not only to maximum doses but also to lower dose-volume levels. Thus, both constraint types should be included as in the dose optimisation process. We also propose the use of the mandible volume as an additional metric to assist in the treatment planning process. Based on our results, D2% could be considered as a surrogate of Dmax, which would encourage the transition from single spatial-point to dose-volume reporting in future published work, as recommended by the ICRU Report 83. PH-0388 Development of guideline for dental care in head and neck cancer patients prior to radiation therapy A. Oladega 1 , D. Mojdami 2 , A. Hope 3,4 , E. Watson 5 , M. Glogauer 5,2 1 Princess Margaret Cancer Centre , Department of Dental Oncology and Maxillofacial Prosthetics, Toronto, Canada; 2 University of Toronto, Faculty of Dentistry, Toronto, Canada; 3 Princess Margaret Cancer Centre, Radiation medicine program, Toronto, Canada; 4 University of Toronto, Department of Radiation Oncology, Toronto, Canada; 5 Princess Margaret Cancer Centre, Department of Dental Oncology and Maxillofacial Prosthetics, Toronto, Canada Purpose or Objective The aim of the study is to develop consensus guidelines for dental care in head and neck cancer patients undergoing radiation therapy using the Modified Delphi Technique. Materials and Methods We invited 44 Canadian dental oncologists to participate as panelists in the study using purposive and snowballing sampling techniques. Three rounds of iterative structured surveys were completed followed by a virtual meeting to conclude the modified Delphi process, from March to December 2020. Questions were divided into six main domains: 1) Radiation dose 2) Dental caries/periapical disease 3) Third molar 4) Periodontal disease 5) Treatment timing and 6) General. Patients were categorized as low, moderate, and high-risk based on factors identified by panelists and agreed upon during the first round. The threshold value set for each round of the Delphi process was a 70% response rate and 75% Consensus level. Round one questions were open-ended to allow participants to express their opinion, which were then used to generate close-ended questions for subsequent rounds. The panelists were able to view the result of the prior round. Results Eighteen panelists out of the forty-four completed the study, with the response rate between each round >70%. The consensus rate achieved during rounds 1, 2, 3 and the virtual meeting were 24%, 62%, 61% and 81% respectively. When considering the radiation dose at which panelists would consider prophylactically extracting teeth to prevent osteoradionecrosis, 83% agreed on 70Gy in the maxilla and 87% agreed on 60Gy in the mandible. Examples of patient risk factors agreed upon to categorize patients as low to high risk included cancer stage and prognosis, oral status and patient compliance with dental care. For teeth with grade III/IV periodontitis, the recommended treatment was extraction regardless of patient risk factors. In general, for teeth with dental caries and periapical disease, treatment recommendations were more aggressive in the mandible > maxilla, posterior > anterior, and high-risk > low- risk patients. Asymptomatic fully impacted or fully erupted third molars should not be extracted, while asymptomatic partially impacted third molars should be extracted when sufficient time allows for healing, ideally, at least 7-14 days of healing. Overall, 94% of panelists agreed that they were confident in their responses throughout the modified Delphi process. Conclusion These national pre-radiotherapy dental guidelines represent the culmination of a year-long modified Delphi process that engaged dental oncologists across Canada. In the future, our goal is to implement and test the impact of these guidelines prospectively through a national multi-center study.

Award lecture: C Regaud Award

SP-0390 Hypofractionation for breast cancer and some other things J. Yarnold 1 1 Institute of Cancer Research, Division of Radiotherapy & Imaging, London, United Kingdom

Abstract Text ESTRO has had an enormous influence on my life starting from its first annual scientific meeting in London in 1982, so it is a very special honour to describe research with a distant connection to Professor Claude Regaud, whose seminal work on fractionation at Institute Curie 100 years ago had such a profound influence on the development of our specialty. My short talk will include two anecdotes from the early years of my career that set me on the hypofractionation trail. This was at a time when adjuvant radiotherapy for patients with early breast cancer and palliative radiotherapy for patients with painful bone metastasis accounted for 50% of treatment resource use in the UK. Two explanatory trials subsequently generated direct estimates of fraction size sensitivity (alpha/beta) for breast cancer unconfounded by time, but it was a pragmatic trial that established a 3-week schedule as standard of care in the UK in 2008 and later more widely. Even when positive trial results are independently reproduced several times, routine adoption even of palliative schedules can take a very long time. Working with patients is always a privilege, but the most stimulating and enjoyable aspect of the last 40 years has been working with multidisciplinary groups of colleagues on clinical trials. This enormous sense of