ESTRO 2020 Abstract Book

S460 ESTRO 2020

cigarette group (21.2%) (p=0.24). There was no difference in the local control rate between with and without chemotherapy or molecular target therapy. In multivariate analyses, relapse rate and DFS of complete cessation group were significantly better than freely cigarette group (HR, 0.63 and 0.26 respectively, p <0.05).

accurate estimation of hearing loss after proton therapy is difficult due to additional intrinsic and extrinsic factors. In order to better estimate the hearing loss to be expected, we retrospectively determined the effect of proton beam irradiation on the hearing function in patients who had skull base tumors. Material and Methods This retrospective study include 51 patients (median age, 48.5 years) with chordoma (n=24), chondrosarcoma (n=15), head and neck tumors (n=9) and meningioma (n=3). There were 21 male and 30 female patients and all underwent PT. All patients had a Pure-Tone Audiometry before and after PT. As a measure for hearing loss the Pure-Tone Average (PTA) of 500Hz, 1.000Hz, 2.000Hz and 4.000Hz was calculated for both ears (n=102) separately. A hierarchical linear mixed-effects model was chosen to simultaneously account for co-variables. Results The median tumor dose was 72 Gy(RBE), (range, 52.2-77.8) and the median dose to the cochlea was 33.9 Gy(RBE) (range, 0.03 – 76.7). At baseline, 23 (22.5%) ears had sensorineural, 4 (3.9%) ears conductive and 7 (6.9%) ears mixed hearing loss. In 20 ears only the air conductivity was measured and the loss of hearing could be caused by obstruction or damage to the outer, middle and/or inner ear. The median PTA before PT (PTA.bl) was 15 dB (IQR 10-25) and the median PTA after PT was 26.25 dB (IQR 11.3 - 45). The median time interval between the end of PT and first audiometry was 279 days. Some patients were followed over a longer period of time with multiple hearing tests. In multivariate analysis, PTA.bl (p=<0.01), mean dose to cochlea (p=<0.01), time since treatment (p=0.01) and age (p=0.02), were independent prognostic factors for hearing loss after PT. Based on these findings, an equation has been derived that predicts the expected hearing loss after treatment: -14.3 + 0.830 * (PTA.bl) + 0.295 * (Age) + 1.686 * (Years since treatment) + 0.307 * (Dmean Cochlea). Conclusion Based on the hearing loss in 51 patients we constructed a predictive model for hearing loss after PT including PTA at baseline, age, time since treatment and mean cochlear dose. The validation of this model must be carried out in a prospective cohort of patients treated with PT/radiotherapy. PO-0855 Radiation-induced meningiomas: outcomes following stereotactic radiosurgery M. Huo 1 , D. Shultz 1 , N. Laperriere 1 , M. Hodaie 2 , M. Cusimano 2 , F. Gentili 2 , D. Payne 1 , A. Berlin 1 , M. Schwartz 2 , B. Millar 1 , G. Zadeh 2 , C. Coolens 3 , D. Tsang 1 1 Princess Margaret Cancer Centre, Radiation Oncology, Toronto, Canada ; 2 Toronto Western Hospital, Neurosurgery, Toronto, Canada ; 3 Princess Margaret Cancer Centre, Radiation Oncology Physics, Toronto, Canada Purpose or Objective Radiation induced meningiomas are a late sequelae of therapeutic cranial radiotherapy, with an incidence of around 20% in patients treated during childhood. Stereotactic radiosurgery is an established treatment option for meningiomas, though limited data exists for radiation-induced lesions. The results of the largest known series of patients treated with radiosurgery to date are A review of data from a prospectively-maintained database was conducted, along with individual chart assessment to obtain additional information. Patients treated with frame-based cobalt-60 radiosurgery between October 2005 and December 2018 were included. Lesions henceforth presented. Material and Methods Poster: Clinical track: CNS

Conclusion We confirmed the significant differences of the local control and survival between the complete smoking cessation patients and freely smoking patients by monitoring expiratory carbon monoxide. We think that the monitoring expiratory carbon monoxide is suitable for clinical working because it can supply answers in real-time and considering the biological effects such as tissue hypoxia. PO-0854 Prediction of sensorineural hearing loss in patients undergoing proton therapy for skull base tumors N. Roos 1 , F. Pfiffner 2 , M. Walser 1 , A. Pica 1 , D. Leiser 1 , U. Kliebsch 1 , S. Von Felten 3 , D.C. Weber 1 , D. Veraguth 2 , B. Bachtiary 1 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen PSI, Switzerland ; 2 University Hospital Zurich, Departement of Otorhinolaryngology- Head and Neck Surgery, Zurich, Switzerland ; 3 University Zurich, Epidemiology- Biostatistics and Prevention Institute, Zurich, Switzerland Purpose or Objective Sensorineural hearing loss is a common complication after radiotherapy in patients with skull base tumors and has a significant impact on the quality of life. Proton therapy (PT) can contribute to reducing the dose to the cochlea and consequently the risk of hearing loss, in particular when a high dose of radiation to the tumor is necessary. Although there are certain guidelines for the threshold dose to the cochlea, in the daily clinical routine an