Purpose: To study pulmonary radiological abnormalities with computer tomography (CT) following different radiotherapy (RT) techniques for breast cancer with respect to regions and density, and their correlation to pulmonary complications and reduction in vital capacity (VC).
Methods and materials: CT scans of the lungs were performed prior to and 4 months following RT in 105 breast cancer patients treated with local or local-regional RT. The radiological abnormalities were analyzed with a CT-adapted modification of a classification system originally proposed by Arriagada, and scored according to increasing density (0-3) and affected lung regions (apical-lateral, central-parahilar, basal-lateral). The highest density grade in each region were added together to form scores ranging from 0-9. The patients were monitored for RT-induced pulmonary complications. VC was measured prior to and 5 months following RT.
Results: Increasing CT scores were correlated with both local-regional RT and pulmonary complications (p < 0.001). The mean reduction of VC for patients scoring 4-9 (-202 ml) was larger than for patients scoring 0-3 (-2 ml) (p = 0.035). The effect of confounding factors on the radiological scoring was tested in the local-regional RT group. Scores of 4-9 were less frequently seen in the patients who had received adjuvant chemotherapy prior to RT. The importance of the respective lung regions on the outcome of pulmonary complications was tested. Only radiological abnormalities in the central-parahilar and apical-lateral regions were significantly correlated to pulmonary complications.
Discussion: Radiological abnormalities detected on CT images and scored with a modification of Arriagada's classification system can be used as an objective endpoint for pulmonary side effects in breast cancer. The described model should, however, be expanded with information about the volume of lung affected in each region before definite conclusions can be drawn concerning each region's relative importance for the development of pulmonary complications. The negative association between sequential chemotherapy and radiological abnormalities should be confirmed in future studies.