ESTRO 38 Abstract book

S197 ESTRO 38

systemic treatment) for head and neck squamous cell carcinomas. Based on treatment planning CT scans, carotid arteries were delineated and dose-volume parameters were calculated bilaterally for the entire carotid arteries (external carotid arteries were excluded) and for the common carotid artery (CCA), bifurcation and internal carotid artery (ICA). ICVEs were scored prospectively and additional information was added by reviewing patient records. Cox proportional hazards analysis was performed to analyse the relationship between radiation dose and the risk of ICVE. Results In the univariate analysis, anterior circulation ICVE risk was significantly associated with dose variables to the entire carotid arteries, particularly to the CCA and the bifurcation. Multivariable analysis showed that the absolute volume (cc) of the entire carotid arteries that receives at least a radiation dose of 10 Gy was the most important prognostic factor for ICVE (Figure 1), with a HR of 1.14 per cc (95% CI 1.064-1.222; p<0.001). No relevant confounding patient and treatment characteristics were found, meaning that the absolute V10 to the entire carotid arteries can be considered as an independent prognostic factor for the cumulative incidence of ICVE.

Purpose or Objective The authors aimed to evaluate treatment outcome of primary and postoperative radiotherapy (RT) for 265 sinonasal adenoid cystic carcinomas, the currently available largest single-center patient collective for this cohort. Material and Methods 265 patients who received either an intensity modulated radiotherapy (IMRT) alone or a dose-escalated bimodal treatment with IMRT and carbon ion boost for sinonasal adenoid cystic carcinoma at the Department of Radiation Oncology, University Hospital Heidelberg and at the Heidelberg Ion-Beam Therapy Center (HIT) between 2003 and 2018 were analyzed retrospectively for local control (LC), distant progression-free survival (DPFS) and overall survival (OS) using Kaplan-Meier estimates. The majority of patients had tumors in advanced stages (T4 stage, n=208, 78.5%) or were irradiated for a macroscopic tumor disease (n=200, 76%). Overall, 35% of the patients received primary (n=93) and 65% postoperative RT (n=172). Additionally, toxicity was assessed according to the Common Toxicity Terminology Criteria for Adverse Events (CTCAE) v5. Results Median follow-up was 49 months. At last follow up, 61% of the patients were still alive (n=90/231) while local recurrence occurred in 38% (n=84/231) and distant relapse in 39% (n=87/231), respectively. In univariate and multivariate analysis, we could identify three prognostic subgroups (postoperative bimodal RT vs. postoperative IMRT vs. definite bimodal RT) resulting in significantly different LC ( p=0.003 ), DPFS ( p=0.005 ) and OS rates ( p<0.0001 ). Best survival outcome could be achieved for the postoperative bimodal RT subgroup with a 5-year OS and DPFS of 78% and 72% vs. 69% and 70% for postoperative IMRT vs. 60% and 50% for definite bimodal RT, respectively. Bimodal RT resulted in a significantly increased LC compared to IMRT alone with a 5-year LC rate of 82% for postoperative bimodal RT vs. 76% for definite bimodal RT vs. 58% for postoperative IMRT alone. The majority of recurrences occurred in-field (n=37/84, 44%) and at critical structures where dose was spared (n=34/84, 40%). Toxicity was moderate with 29% acute and 16% late grade 3 toxicity. Conclusion The authors conclude that bimodal RT in a primary or postoperative setting results in superior LC rates with moderate toxicity. Nevertheless, regarding overall survival outcome including OS, LC and DPFS, patients may profit the most from postoperative dose-escalated bimodal RT. OC-0392 Risk of ischemic cerebrovascular events is associated with carotid artery radiation dose E. Van Aken 1 , H. Bijl 1 , H.P. Van der Laan 1 , L. Van den Bosch 1 , A. Van den Hoek 1 , M. Dieters 1 , R. Steenbakkers 1 , H. Langendijk 1 1 University Medical Center Groningen, Radiation Oncology, Groningen, The Netherlands Purpose or Objective Radiotherapy in the head and neck area may cause vascular damage to the carotid arteries, increasing the risk of ischemic cerebrovascular events (ICVEs). However, limited data exists on the relationship between radiation dose and the risk of ICVE. This information is crucial to identify patients at risk and to optimize radiotherapy treatment plans. Therefore, the purpose of this study was to determine the relationship between radiation dose to the carotid arteries and anterior circulation ICVE risk and to identify the most relevant dose-volume parameters. Material and Methods A retrospective analysis was performed using data of a prospective cohort study of 750 patients treated with definitive radiotherapy (either or not combined with

Conclusion This is the first prospective cohort study that demonstrates an independent dose-effect relationship between radiation dose to the carotid arteries and the risk of ICVE. These findings may lead to more adequate ICVE risk prediction and prevention in these patients. ICVE prevention can be achieved by radiotherapy treatment optimization, regular screening or pharmacological treatment. OC-0393 Impact of sarcopenia on survival and late toxicity in head and neck cancer patients treated with RT I. Van Rijn - Dekker 1 , L. Van den Bosch 1 , A. Van den Hoek 1 , H. Bijl 1 , M. Dieters 1 , E. Van Aken 1 , H.P. Van der Laan 1 , H. Langendijk 1 , R. Steenbakkers 1