ESTRO 2022 - Abstract Book

S431

Abstract book

ESTRO 2022

risk that can be considered during RT planning because of a risk for toxicities. The current study aimed to investigate if the high dose clinical target volumes (CTV1) and planning target volume (PTV1) affected the risk and severity of acute mucositis (AM) for patients treated for head and neck squamous cell carcinomas (HNSCC) at three centres. Materials and Methods The cohort consisted of patients treated for squamous cell carcinomas of the oropharynx, hypopharynx, and larynx (except T1 glottis) according to DAHANCA radiotherapy guidelines using accelerated (66-68 Gy/33-34fx, 6 fx/week) or hyperfractionated (76-78 Gy/56-fx, 10 fx/week) RT ± systemic treatment and/or radiosensitiser in three DAHANCA centres between 2010 and 2015. Mucosal reactions were scored weekly during RT, as well as 2 weeks after RT as 0: none, 1: erythema, 2: patchy mucositis, 3: confluent mucositis, 4: ulceration. The highest observed score was used as the endpoint. Acute mucositis dependence was tested using ordinal logistic regression analysis, hence, all grades of AM were used. Predictors available for the model were: sex (male/female), age, smoking status (never/former/current/missing), primary tumour site (oropharynx/ hypopharynx/larynx), stage (1-2/3-4), systemic treatment (+/-), RT dose (66,68/76,78 Gy), radiosensitiser (+/-), and CTV1 volume (cm 3 ) as continuous variable. The analysis was also performed with the same parameters where CTV1 was replaced by PTV1. Parameter selection was done through backward selection. Results A total of 1,623 patients received treatment. The median CTV1 volume was 55 cm 3 (IQR 34-92 cm 3 ) ; and PTV1 - 120 cm 3 (IQR 79-186 cm 3 ). Twenty-one patients had no AM recorded, and the majority (n=1,479 (91.2%)) had grade 2 or 3 AM. Statistically significant factors related to acute mucositis were: CTV1 (OR 1.003 per cm 3 [95%CI 1.001-1.005]), female (OR 1.5[1.1-2.0]), oropharyngeal cancers (OR 3.0[2.3-4.0]), higher RT doses (OR 2.5 [1.6-4.0] and the use of systemic therapy (OR 1.4 [1.1-1.8] (Figure). Age, smoking status, stage, and radiosensitiser were not found to influence the risk of AM. A very similar result was found when CTV1 volume was substituted with PTV1.

Conclusion AM is directly dependant on the CTV1 target volume. An increase in high dose radiotherapy treatment volumes for HNSCC patients will result in an increased risk of acute mucositis.

MO-0481 Mandibular osteoradionecrosis after postoperative radiotherapy for oral cavity cancer

M. Möring 1,2,3 , H. Mast 2 , E. Wolvius 2 , G. Verduijn 1 , S. Petit 1 , N. Sijtsema 1,4 , B. Jonker 2 , R. Nout 1 , W. Heemsbergen 1

1 Erasmus MC Cancer Institute, Erasmus University Medical Center, Radiotherapy, Rotterdam, The Netherlands; 2 Erasmus University Medical Center, Oral and Maxillofacial Surgery, Rotterdam, The Netherlands; 3 Da Vinci Clinic, Hyperbaric Oxygen Therapy, Rotterdam, The Netherlands; 4 Erasmus University Medical Center, Radiology and Nuclear Medicine, Rotterdam, The Netherlands Purpose or Objective Osteoradionecrosis (ORN) of the mandible is a severe late complication of external beam radiotherapy (EBRT) for oral cavity cancer (OCC) that is difficult to manage and can have a significant impact on quality of life. Several risk factors for the development of ORN for head and neck cancers have been identified, however, knowledge of risk factors for ORN after postoperative EBRT (PORT) for OCC is limited. The goal of this study was to describe the incidence and determine risk factors of mandibular ORN in patients treated with PORT for OCC. Materials and Methods All OCC patients (N=227) treated with PORT at the Erasmus Medical Center between 2010 and 2018, with a minimum of one year disease free follow-up, were included in a retrospective cohort. The median age was 66 (range 24-91), 58.6% was male, and 48.9% of the primary surgeries involved a marginal or segmental mandible resection. Frequently prescribed dose schedules were 33x2Gy (49.3%) and 30x2Gy (27.8%). Follow-up was censored at the first of the following events: end of follow-up (standard follow-up 5 years), death, disease recurrence or additional head and neck RT. Dose-volume data were extracted from treatment plans. Cumulative incidence rates of mandibular ORN were computed using the Kaplan Meier method. Risk factors for the development of mandibular ORN were evaluated with Cox regression models (uni- and multivariable).