Determinants of Cardiorespiratory Fitness Following Thoracic Radiotherapy in Lung or Breast Cancer Survivors.

We measured peak oxygen consumption (VO) in previous recipients of thoracic radiotherapy and assessed the determinants of cardiorespiratory fitness with an emphasis on cardiac and pulmonary function. Cancer survivors who have received thoracic radiotherapy with incidental cardiac involvement often experience impaired cardiorespiratory fitness, as measured by reduced peak VO, a marker of impaired cardiovascular reserve. We enrolled 25 subjects 1.8 (0.1 to 8.2) years following completion of thoracic radiotherapy with significant heart exposure (at least 10% of heart volume receiving at least 5 Gray). All subjects underwent cardiopulmonary exercise testing, Doppler echocardiography, and circulating biomarkers assessment. The cohort included 16 Caucasians (64%), 15 women (60%) with a median age of 63 (59 to 66) years. The peak VO was 16.8 (13.5 to 21.9) ml·kg·min or moderately reduced at 62% (50% to 93%) of predicted. The mean cardiac radiation dose was 5.4 (3.7 to 14.7) Gray, and it significantly correlated inversely with peak VO (R = -0.445, p = 0.02). Multivariate regression analysis revealed the diastolic functional reserve index and the N-terminal pro-brain natriuretic peptide (NTproBNP) serum levels were independent predictors of peak VO (ß = +0.813, p <0.01 and ß = -0.414, p = 0.04, respectively). In conclusion, patients who had received thoracic radiation display a dose-dependent relation between the cardiac radiation dose received and the impairment in peak VO, the reduction in diastolic functional reserve index, and elevation of NTproBNP.