ESTRO 2021 Abstract Book

S280

ESTRO 2021

achievable dose volume histograms (DVHs) for individual organs at risk (OARs) of new patients; this has the capability to remove the subjective nature of the radiotherapy planning process and reduce optimisation time. Combining RapidPlan models from different centres could have the potential to improve the quality, efficiency and consistency of radiotherapy treatments across the UK. The Distributed RapidPlan platform, currently in prototype form, allows multiple RapidPlan models to be combined between centres to create a ‘super-model’ using their collective patient libraries, thus increasing the breadth of knowledge and statistics available to the model for training and therefore its applicability and potential success clinically. Materials and Methods A head and neck ‘super-model’ was created by merging the data libraries of three UK centres and training a RapidPlan model on the merged data set. A mutually-agreed set of objectives were established and used as the model template from which to build the ‘super-model’. The ‘super-model’ was validated on 10 head and neck patients from four UK centres and the generated plans were assessed using established plan evaluation criteria: D99%, D50%, D2% for PTVs, and mean and maximum doses for OARs. Results The RapidPlan ‘super-model’ successfully generated plans that passed the established plan evaluation dose objectives for all patients with single optimisations in a total average optimisation and calculation time of 12 minutes. OAR sparing was significantly improved by implementing the ‘super- model’, with a mean parotid dose reduction of 5.38 ± 2.51 Gy, a mean spinal cord dose reduction of 4.59 ± 0.93 Gy and a mean brainstem dose reduction of 1.38 ± 1.72 Gy. PTV coverage achieved the established constraints but was reduced compared with clinical plans, with a mean primary PTV D99% reduction of 1.11 ± 0.16 Gy and a mean elective PTV D99% reduction of 0.57 ± 0.15 Gy. Conclusion The Distributed RapidPlan platform allowed three centres to successfully merge their patient libraries to create a ‘super-model’ capable of generating plans that met the plan evaluation criteria for head and neck patients with improvements in OAR sparing. The primary indications are that the ‘super-model’ will improve head and neck planning quality, efficiency and consistency across centres in the UK. PH-0382 Radiotherapy as nose preservation treatment for cancer of the nasal vestibule: the Dutch experience M. Czerwinski 1 , P. Jansen 2 , E. Zwijnenburg 1 , A. Al-Mamgani 3 , M. Vergeer 4 , J. Langendijk 5 , F. Wesseling 6 , J. Kaanders 7 , C. Verhoef 1 1 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands; 2 Erasmus University Medical Center, Radiation Oncology, Rotterdam, The Netherlands; 3 Netherlands Cancer Institute/Antoni van Leeuwenhoek, Radiation Oncology, Amsterdam, The Netherlands; 4 Amsterdam University Medical Center, Radiation Oncology, Amsterdam, The Netherlands; 5 University Medical Center Groningen, Radiation Oncology, Groningen, The Netherlands; 6 Maastricht University Medical Center (MAASTRO), Radiation Oncology, Maastricht, The Netherlands; 7 Radboud University Medical Center, Radiation Oncology, Nijmegen, The Netherlands Purpose or Objective Cancer of the nasal vestibule (CNV) is a rare form of squamous cell carcinoma. Due to its discernible location, CNV is often diagnosed early, in Wang T1-T2 stage. Both surgery and radiotherapy provide good oncologic results for early stage tumors. However, primary radiotherapy is often preferred for preservation of cosmesis and nasal function. Another important consideration in primary CNV treatment should be prevention of mutilating salvage nose amputations. Due to practice variation and the absence of comparative trials, no consensus is established on preference for either brachytherapy (BT) or external beam radiotherapy (EBRT). Therefore, the purpose of this study was to compare BT and EBRT in terms of disease control, nose preservation and toxicity. An additional objective was to investigate prognostic factors for relapse. Materials and Methods Medical records of 225 patients with Wang T1-T2 cancer of the nasal vestibule treated with 3D image-guided primary radiotherapy between Jan 2010 and Dec 2016 in 6 Dutch university medical centers were retrospectively reviewed. Main outcomes were actuarial 3-year local control (LC), regional control (RC), disease-specific survival (DSS), overall survival (OS), survival with preserved nose (SPN) and 5-year late radiation toxicity free survival scored by CTCAE 5.0 criteria. Results 153 of 225 patients were treated with BT, 65 with EBRT, and 7 using other modalities. Median follow-up was 46 months. Overall 3-year LC and RC were 87% and 89%, respectively. Five-year DSS and OS were 94% and 82%. Three-year SPN was 76%. BT provided significantly higher 3-year LC (95% vs 71%, p<0.01; fig 1) and 3-year SPN rates compared with EBRT (82% vs 61%, p<0.01; fig 1). Multivariable analysis confirmed better outcomes with BT (table 1). No difference was found in 3-year RC and OS and DSS rates. Late radiation toxicity was reported more frequently after BT. Five-year grade ≥2 toxicity free survival was worse after brachytherapy compared to external beam radiotherapy (80% vs 97%, p=0.03), due to higher incidence of grade 2 radiation ulcers. Incidence of chondritis and septal defects did not differ. Half of all late sequalae recovered with or without treatment. Additionally, tumor diameter ≥1.5cm and T2-stage significantly increased risk of regional recurrence (table 1). Figure 1: univariable local control and survival with preserved nose for BT vs EBRT Poster highlights: Poster highlights 14: Head and neck 2