ESTRO 2022 - Abstract Book

S746

Abstract book

ESTRO 2022

Results One hundred and four consecutive patients were included (mean age 63 years, range 25-87), of which 68 were males and 36 females. Among clinical factors, only the age was found to be correlated to the outcome. Table 1 reports the performing value of Vdose for each mastication structure and its significance level. Multivariate analysis showed that V42.3 Gy of the coronoid process and the V50.3 Gy of the medial pterygoid muscles were not significantly cross related.

Conclusion High radiation doses to the choroid process (V42 Gy) and medial pterygoid muscles (V50 Gy) correlates with mouth opening reduction after radiotherapy

PD-0828 Risk factors for the development of maxillary osteoradionecrosis in ACC patients treated with CIRT

B. Vischioni 1 , S. Russo 1 , M. Meuli 1 , S. Ronchi 1 , R. Ingargiola 1 , A. Ferent 2 , S. Imparato 3 , L. Preda 4 , M. Ciocca 2 , M. Bonora 2 , S. Molinelli 2 , E. Orlandi 2 1 CNAO National Center for Oncological Hadrontherapy, Clinical Depatment, Pavia, Italy; 2 CNAO National Center for Oncological Hadrontherapy, Clinical Department, Pavia, Italy; 3 CNAO National Center for Oncological Hadrontherapy, Radiology Department, Pavia, Italy; 4 San Matteo Hospital, Radiology Department, Pavia, Italy Purpose or Objective The present study aims to evaluate dosimetric and clinical risk factors for the development of maxillary osteoradionecrosis (ORN) in head and neck adenoid cystic carcinoma (ACC) patients treated with carbon ion radiotherapy (CIRT). Materials and Methods Clinical data and treatment plans of ACC patients, consecutively treated from January 2013 to October 2016 within the phase II clinical trial CNAO S9/2012/C, were retrospectively reviewed. ORN and other treatment-related toxicities were graded according to the Common Terminology Criteria for Adverse Events (CTACE) scale. The maxillary bone was contoured on the planning CT, and only patients receiving more than 10% of the prescription dose at their maxilla were considered for the analysis (67 patients). The volumes of maxilla receiving doses from 10 Gy (RBE) to 60 Gy (RBE) (V D ), with an increment of 10 Gy (RBE), and additional clinical factors were correlated to the incidence of ORN with univariate analysis (Chi-square test). The Cox regression model was subsequently applied for multivariate analysis. Treatment plans calculated with a local effect model (LEM) –based optimization were recalculated with the modified microdosimetric kinetic model (MKM), and compared with literature data from the Japanese experience. Results The median time interval from the start of CIRT to ORN appearance was 24 months (range, 8 - 48 months). Maxillary ORN was observed in 11 patients (16%). Grade 1 ORN was observed in 2 patients (18%), G2 in 3 (27%), G3 in 4 (36%) and G4 in 2 patients (18%). At univariate analysis, the presence of maxillary elements within the PTV and acute mucositis correlated with the development of maxillary ORN. V D were significantly higher for all dose levels tested in patients with maxillary ORN than in patients without (Figure1), according to both radiobiological models. At multivariate analysis V50 significantly correlated with ORN.