No Increased Cardiac Mortality or Morbidity of Radiation Therapy in Breast Cancer Patients After Breast-Conserving Surgery : 20-Year Follow-up of the Randomized SweBCGRT Trial

Purpose: Radiation therapy (RT) after breast-conserving surgery reduces locoregional recurrences and improves survival but may cause late side effects. The main purpose of this paper was to investigate long-term side effects after whole breast RT in a randomized clinical trial initiated in 1991 and to report dose-volume data based on individual 3-dimensional treatment plans for organs at risk. Methods and Materials: The trial included 1187 patients with T1-2 N0 breast cancer randomized to postoperative tangential whole breast RT or no further treatment. The prescription dose to the clinical target volume was 48 to 54 Gy. We present 20-year follow-up on survival, cause of death, morbidity, and later malignancies. For a cohort of patients (n = 157) with accessible computed tomography–based 3-dimensional treatment plans in Dicom-RT format, dose-volume descriptors for organs at risk were derived. In addition, these were compared with dose-volume data for a cohort of patients treated with contemporary RT techniques. Results: The cumulative incidence of cardiac mortality was 12.4% in the control group and 13.0% in the RT group (P = .8). There was an increase in stroke mortality: 3.4% in the control group versus 6.7% in the RT group (P = .018). Incidences of contralateral breast cancer and lung cancer were similar between groups. The median Dmean (range) heart dose for left-sided treatments was 3.0 Gy (1.1-8.1), and the corresponding value for patients treated in 2017 was 1.5 Gy (0.4-6.0). Conclusions: In this trial, serious late side effects of whole breast RT were limited and less than previously reported in large meta-analyses. We observed no increase in cardiac mortality in irradiated patients. Doses to the heart were a median Dmean of 3.0 Gy for left-sided RT. The observed increase in stroke mortality may partly be secondary to cardiac side effects, complications to anticoagulant treatment, or to chance, rather than a direct side effect of tangential whole breast irradiation