ESTRO 2020 Abstract Book

S172 ESTRO 2020

patients received an additional tumor bed boost after BCS. Systemic treatment consisted of endocrine therapy (47%), chemotherapy (19%) or both (34%). Patients were followed with clinical examination every six months for the first five years after treatment, and once yearly in the following five years. Beyond 10 years, patient vital status was monitored in the DBCG registry. The effect of IMNI on OS was assessed in the entire cohort and within sub-groups defined by pN-stage and tumor location. All analyses were performed by intention to treat. Results With a median of 14.3 years of follow-up time, 551 of 1,492 patients with right-sided and 664 of 1,597 patients with left-sided breast cancer had died. The 14-year OS rates were 62.1% with IMNI versus 57.6% without IMNI. The adjusted hazard ratio (HR) for death was 0.85 (95% CI, 0.76 to 0.95; p=0.005). In subgroup analysis, for a lateral tumor with pN1 stage, the estimated HR for death was 0.98 (95% CI, 0.78 to 1.23) with vs. without IMNI. Estimates were lower for the remaining sub-groups: Medial/central tumor and pN1 stage: HR=0.78 (95% CI, 0.61 to 1.00), lateral tumor and pN2-3 stage: HR=0.78 (95% CI, 0.64 to 0.95), medial/central tumor and pN2-3 stage: HR=0.90 (95% CI, 0.71 to 1.14). No heterogeneity of effect between subgroups was detected.

changed from 2D to 3D-based. The aim of this study was to evaluate the risk of coronary artery stenosis requiring intervention among early stage breast cancer patients treated with adjuvant RT. Material and Methods Women diagnosed with early stage breast cancer in Denmark between 1990-2016 were identified from the register of the Danish Breast Cancer Group. The registry contains information on patient, tumor and treatment characteristic. Information of coronary artery stenosis was collected from The Western Denmark Heart Registry, which contains information on all invasive cardiac procedures performed in Jutland and Funen. Coronary artery stenosis was defined as clinical relevant and included if the degree of stenosis was at least 50%. Patients with stage IV disease at the diagnosis of breast cancer, prior cancer, bilateral or unknown laterality of breast cancer, or treatment not involving surgery were excluded. Incidence rate ratios (IRR) of coronary artery stenosis requiring intervention were calculated by comparing patients irradiated for left versus right-sided breast cancer (LvsR) and stratified by age and years after RT, both in 5 years interval. Results This study included 87,550 breast cancer patients followed for a median of 7 years (746,662 person-years). Among these patients, 42,740 received RT: 51.1% on the left and 48.9% on the right side. Among the patients irradiated, 40% were treated with chemotherapy. Tumor characteristics and oncological treatment were balanced between left and right-sided irradiated patients. Invasive procedures for coronary artery stenosis were preformed in 233 left-sided and 178 right-sided irradiated patients. The IRR for coronary artery stenosis requiring intervention, LvsR, among all irradiated patients was 1.2 (95% CI 0.99 - 1.46) and for patients irradiated before 2008 the IRR LvsR was 1.35 (95% CI 1.02 - 1.77) with the largest risk within the first five years and again after 10 years following RT. For patients treated after 2008 the IRR LvsR was 1.05 (96% CI 0.79; 1.41) with no significant difference in time intervals after RT. No increased IRR LvsR was observed for patients treated with adjuvant chemotherapy, neither before nor To our knowledge this is the largest study investigating radiation associated coronary artery stenosis requiring intervention. RT for left-sided breast cancer was associated with an increased incidence of coronary artery stenosis for patients treated before 2008 whilst no effect from RT was detected in patients treated after 2008. For patients treated with adjuvant chemotherapy no increased risk was observed. OC-0328 APBI can improve survival by reducing the secondary lung cancer risk – How important is the issue? J. Pignol 1 , N. Hoekstra 2 , H. Dahn 1 , D. Wilke 1 1 Dalhousie University, Radiation Oncology, Halifax, Canada ; 2 Erasmus MC, Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective There is an excess risk of secondary lung cancer (SLC) after breast radiotherapy (RT), and we previously modeled an increased absolute lifetime risk of 3.8% for a patient treated at age 50 years, which translates into a 3% long- term excess mortality risk. This risk raises steeply after 20 to 25 years and is linked to the mean lung dose, which depends on the radiotherapy technique. The aim of this after 2008. Conclusion

Conclusion IMNI provided a long-lasting and significant gain in OS in all patients with node-positive early breast cancer regardless of pN-stage and tumor location. OC-0327 Radiotherapy associated coronary artery stenosis in 87,550 patients with early stage breast cancer M.L.H. Milo 1 , L.B.J. Thorsen 1,2 , J. Alsner 1 , K.M. Nielsen 3 , S.P. Johnsen 4 , B.V. Offersen 1,5,6 1 Aarhus University Hospital, Department of experimental clinical oncology, Aarhus, Denmark ; 2 Aalborg University Hospital, Department of Oncology, Aalborg, Denmark ; 3 Aarhus University Hospital, Department of cordiology, Aarhus, Denmark ; 4 Danish Center for Clinical Health Services Research, Department of Clinical Medinine, Aalborg, Denmark ; 5 DCPT, Danish Center for Particle Therapy, Aarhus, Denmark ; 6 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark Purpose or Objective Adjuvant radiotherapy (RT) to breast cancer patients often causes an incidental radiation dose to the heart with subsequent risk of radiation associated heart disease. In 2008 changes in the systemic treatment (taxanes, herceptin and letrozole) were introduced and RT planning