ESTRO 2020 Abstract Book

S54 ESTRO 2020

increased risk of cardiovascular disease (CVD). Breast cancer patients with pre-existing CVD risk factors have the highest risk of treatment induced cardiotoxicity. Coronary artery calcium (CAC) is a strong independent CVD risk factor and can be quantified on dedicated cardiac computed tomography (CT) scans. Before adjuvant treatment with radiotherapy, a CT scan of the chest is performed for radiotherapy treatment planning. These CT scans allow routinely assessing CAC scores in breast cancer patients, and thereby detecting patients at increased CVD risk. In the Bragatston study, we evaluate the association between automatically measured CAC on radiotherapy planning CT scans and the risk of CVD events in breast cancer patients. Material and Methods In this multicenter historical cohort study, breast cancer patients receiving radiotherapy between 2005-16 were included. CAC scores were automatically extracted from the planning CT scan using an in house developed deep learning algorithm and categorized following the five-level scale Agatston classification (0, 1-10, 11-100, 101-399, >400 units). Tumor and treatment characteristics were obtained from the Netherlands Cancer Registry, the Netherlands Comprehensive Cancer Organisation. Data on occurrence of CVD were obtained from Dutch Hospital Data (DHD) and the National Cause of Death Register, Statistics Netherlands. Cox proportional hazard regression models were used to evaluate the association between CAC scores and CVD events, adjusted for age and calendar year at planning CT. Results Data from 14,034 patients were included. The mean age at the planning CT was 58 years (SD=11). Twenty-eight percent of the patients had a CAC score of >0 (Table 1). Over a median follow-up time of 52 months (IQR: 27-82), 8.2% of the patients (n=1148) were admitted to the hospital for CVD events and 93 patients (0.7%) died from this disease. After adjustment for age and calendar year at planning CT, the incidence of CVD events increased with higher CAC scores (CAC 1-10 HR=1.3, 95%CI:1.0-1.5; CAC 11-100 HR=1.7, 95%CI:1.5-2.1; CAC 101-400 HR=2.2, 95%CI:1.7-2.7; CAC >400 HR=3.7, 95%CI:2.9-4.6).

Conclusion A non-statistically significant trend was demonstrated between toxicity and change in ADC in all PGs and SMGs – more severe late xerostomia was more likely in patients with a smaller ADC rise in those glands, this pattern met statistical significance in the left PG only. This signal will be evaluated further in a larger dataset on completion of the MeRInO study. As strategies to reduce toxicity after H&N RT continue to be investigated, serial evaluation of ADC in salivary glands during treatment may allow a biologically adaptive treatment strategy for those identified to be most at risk of late severe toxicity. OC-0109 Cardiovascular risk assessment based on cardiac calcifications on breast RT planning CT scans R. Gal 1 , I. Išgum 2,3,4 , S.G.M. Van Velzen 2,4 , M.J. Emaus 1 , D.H.J.G. Van den Bongaard 5 , M.L. Gregorowitsch 1 , E.L.A. Blezer 1 , S.A.M. Gernaat 6 , N. Lessmann 2 , M.G.A. Sattler 7 , A.J. Teske 8 , J. Penninkhof 7 , H. Meijer 9 , J.J. Van Tol- Geerdink 9 , J. Pignol 10 , J. Verloop 11 , H.M. Verkooijen 1 1 University Medical Center Utrecht- University of Utrecht, Division of Imaging and Oncology, Utrecht, The Netherlands ; 2 University Medical Center Utrecht- University of Utrecht, Image Sciences Institute, Utrecht, The Netherlands ; 3 Amsterdam University Medical Center, Department of Radiology and Nuclear Medicine, Amsterdam, The Netherlands ; 4 Amsterdam University Medical Center, Department of Biomedical Engineering and Physics, Amsterdam, The Netherlands ; 5 Amsterdam University Medical Center, Department of Radiation Oncology, Amsterdam, The Netherlands ; 6 Karolinska Institutet, Department of Oncology-Pathology, Stockholm, Sweden ; 7 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands ; 8 University Medical Center Utrecht- University of Utrecht, Department of Cardiology, Utrecht, The Netherlands ; 9 Radboudumc, Department of Radiation Oncology, Nijmegen, The Netherlands ; 10 Dalhousie University, Department of Radiation Oncology, Halifax- Nova Scotia, Canada ; 11 Netherlands Comprehensive Cancer Organisation, Department of Research, Utrecht, The Netherlands Purpose or Objective With improved breast cancer survival, the prevention of treatment-induced toxicity is becoming increasingly important. Adjuvant treatments including anthracyclines, targeted and radiotherapy are associated with an

Conclusion CAC detected on the radiotherapy planning CT is strongly associated with an increased risk of CVD events. This finding is relevant for breast cancer patients since early identification of high risk patients enables switching to less cardiotoxic breast cancer treatment (e.g. adaptation of radiotherapy target volumes or technique, chemotherapy dose reduction). Also, patients can adopt targeted cardio- preventive interventions (e.g. lifestyle changes, pharmaco-prevention, close monitoring for early detection of cardiotoxicity). Hence, the burden of CVD in breast cancer survivors can be reduced and better overall survival rates can be achieved. OC-0110 Normal tissue complication probability during proton therapy for head & neck cancer patients E. Van Weerd 1 , J. Jacobs 1 , S. Hutschemaekers 1 , M. Kroesen 1 , Y. Klaver 1 , M. Rodrigues 1 , H. Werz 1 , F. Keskin- Cambay 1 , M. De Jong 1 , R. Wiggenraad 1 , M. Hoogeman 1 , S. Habraken 1 , M. Van Vulpen 1 , J. Zindler 1