ESTRO 2021 Abstract Book

S839

ESTRO 2021

Conclusion Stage I squamous cell carcinoma of the EAC could be cured with 60–66 Gy radiotherapy alone. In contrast, prognosis was poor in patients with stage IV squamous cell carcinoma of the EAC treated with radiotherapy alone and combination with chemoradiotherapy improved OS in these patients. PO-1010 Re-irradiation for head and neck cancer: Cumulative dose and the correlation to carotid blowout A. Embring 1,2 , E. Onjukka 3,2 , C. Mercke 1,4 , I. Lax 3 , A. Berglund 5 , S. Bornedal 6 , B. Wennberg 6 , E. Dalqvist 6 , S. Friesland 1,4 1 Karolinska University Hospital, Department of Oncology, Stockholm, Sweden; 2 Karolinska Institute, Department of Oncology-Pathology, Stockholm, Sweden; 3 Karolinska University Hospital, Medical Radiation Physics and Nuclear Medicine, Stockholm, Sweden; 4 Karolinska Institute, Department of Oncology-Pathology , Stockholm, Sweden; 5 Epistat Epidemiology and Statistics Consulting, Epistat Epidemiology and Statistics Consulting, Uppsala, Sweden; 6 Karolinska University Hospital, Medical Radiation Physics and Nuclear Medicine , Stockholm, Sweden Purpose or Objective Re-irradiation for recurrent head and neck cancer is a treatment option shown to offer long-lasting local control and sometimes even cure for selected patients. However, re-irradiation in the head and neck area is challenging due to the proximity of several vital organs at risk (OAR) and the normal tissue tolerance. In the literature there are several studies proposing dose constraints in the primary setting, but dose constraints in the re-irradiation setting are scarce and there are only a limited number of studies on re-irradiation presenting dose/volume data. This study aims to contribute with valuable dose/volume data on cumulative dose to the carotid arteries and the correlation to carotid blowout syndrome. Materials and Methods Fifty-four consecutive patients re-irradiated for HNC between 2011-2017 in our institution were retrospectively analysed. Data on side effects were collected from a local quality registry and supplemented with a review of medical records. The carotid arteries were delineated on the re-treatment computed tomography (CT) for all included patients. Initial and re-treatment treatment plans were collected, and the 3D dose distributions converted to EQD2. A plan sum was then calculated following a non-rigid registration of the CT images, yielding the cumulative doses to OAR. For each patient, only the carotid doses from the side that received the highest cumulative doses (i.e. only right or left) are reported. Carotid blowout syndrome was defined as a major bleeding from the pharynx in absence of local recurrence. All doses are reported in EQD2. Results The overall survival at 2 and 5 years was 42.6 and 27.3% respectively, and progression free survival at 2 and 5 years was 32.5 and 28.5% respectively. The median follow-up time after re-irradiation was 54.1 months (range 34.3-66.3) in surviving patients and 20.1 months (range 0-69.9) in all included patients. There were two cases of fatal carotid blowout and these events occurred 15 and 38 months after re-irradiation. The cumulative median near-maximum dose (D1cc) to the carotid arteries was 97 Gy (range 47-139 Gy). The composite dose/volume histograms show maximum doses to the carotid arteries to be near or above the third quartile for the two patients experiencing carotid blowout, implying higher cumulative maximum doses in these patients. ROC-curve for logistic regression model on maximum doses to the carotid arteries correlated to carotid blowout showed AUC 0.92 (95% CI 0.83-1.00) and a cut off value of 119 Gy (sensitivity 1.00/specificity 0.89). In the eleven patients without disease at closure of our data base, the majority (64%) had experienced no severe late side effects 2 years after re-irradiation.