ESTRO 2020 Abstract book

S109 ESTRO 2020

uncertainty, dose maps were blurred by a 2D‐Guassian function with width described by the PSF. Permutation testing was used to identify regions where excess dose resulted in worse patient survival with the T‐ map calculated. A threshold was set at the 99 th percentile of the T‐map and the dose from the cardiac surface each patient received extracted for analysis in a multi‐variable cox‐proportional hazards survival model. Results All surface maps were blurred with 2D‐Guassian filter of size σ φ =4.3° and σ y = 1.3 units. Permutation testing for patients dead and alive at 6,12,18 and 24 months showed significant differences, p<0.001. The T‐map for 18 months is included as figure 1 highlighting the highest significance region at the base of the heart and extending into the right and left atria. The mean dose to the region defined by the 99 th percentile across all patients was 21.6Gy compared to the mean dose to the heart of 12.7Gy. Table 1 shows the multi‐variable analysis where the dose to this region on the heart surface is significantly associated with survival, hazard ratio 1.014 per Grey, p=0.03, controlling for covariates including tumour volume.

Purpose or Objective Patients with left‐sided breast cancer have an increased risk of developing cardiovascular disease (CVD) after radiotherapy (RT). While the awareness of cardiac toxicity through irradiation has increased enormously over the last decade, the role of individual baseline cardiac risks has not yet been systematically investigated. Aim of the present study was to evaluate the impact of baseline CVD risks on radiation‐induced cardiac toxicity. Material and Methods 210 patients with left‐sided breast cancer treated in the prospective Save‐Heart Study using a modern heart sparing technique (deep inspiration breath‐hold, DIBH), were analysed regarding baseline risk factors for CVD. Three frequently used prediction tools (Procam, Framingham and Reynolds score) were applied to evaluate the individual CVD risk profiles. Moreover, 10‐year CVD excess absolute risks (EAR) were estimated using the individual mean heart dose (MHD) of treatment plans in free breathing and DIBH. Results The individual baseline CVD risk factors had a strong impact on the 10‐year cumulative CVD risk. The mean baseline risks of the non‐diabetic cohort non‐diabetic cohort (n=200) ranged from 3.11% to 3.58%, depending on the risk estimation tool (3.11% ±5.14% Procam score; 3.39% ±3.67% Framingham score; 3.58% ±4.70% Reynolds score). A large number of the non‐diabetic patients had a very low 10‐year CVD baseline risk of ≤1%. Nevertheless, 8‐9% of patients reached ≥10% baseline 10‐year CVD risk. In contrast, diabetic patients (n=10) had significantly higher baseline CVD risks (11.76% ±12.43% Procam score; 24.23% ±14.59% Framingham score; 10.66% ±9.46% Reynolds score). Regarding radiation‐induced CVD risks, the mean 10‐year cumulative risk (Framingham score) following RT was 3.73% using the heart‐sparing DIBH‐technique (MHD: 1.42Gy) and 3.94% in free breathing (MHD: 2.33Gy), after adding a 10‐year EAR of +0.34% (DIBH) and +0.55% (FB) to the baseline risks, respectively. Smoking status was one of the most important and modifiable baseline risk factors for CVD. After DIBH‐RT, the 182 non‐smoking patients had a mean 10‐year cumulative risk of 3.55% (3.20% baseline risk, 0.35% EAR) as compared to 6.07% (5.60% baseline risk, 0.47% EAR) for the 28 smokers.

Conclusion We successfully created a modified cylindrical polar coordinate system for mapping radiotherapy dose to the heart. Surface maps identified a region near the base of the heart where excess dose results in worse patient survival. This region extends over the left and right atria close to the path of the coronary arteries suggesting these sub‐structures are driving this effect. OC-0198 Heart sparing radiotherapy in breast cancer: the importance of baseline cardiac risks S. Schönecker1, A. Gaasch 1 , C. Simonetto 2 , M. Eidemüller 2 , D. Reitz 1 , M. Pazos 1 , M. Rottler 1 , P. Freislederer 1 , M. Braun 3 , N. Harbeck 4 , M. Niyazi 1 , C. Belka 1 , S. Corradini 1 1 LMU Munich, Department of Radiation Oncology, Munich, Germany ; 2 Helmholtz Center Munich, Institute of Radiation Medicine, Munich, Germany ; 3 Red Cross Hospital, Department of Obstetrics and Gynecology- Breast Centre, Munich, Germany ; 4 LMU Munich, Department of Obstetrics and Gynecology- Breast Centre, Munich, Germany

Conclusion In the present study, three different clinically applicable CVD prediction tools were used, which all showed comparable results and can be easily integrated into daily clinical routine in radiation oncology. A systematic evaluation and screening could identify patients with high baseline CVD risk factors who may benefit from primary prevention through counselling or pharmacotherapy interventions. As shown in the present study, this could result in a much higher benefit than from heart‐sparing irradiation techniques alone.

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