Prediction of Ipsilateral Lung Doses in Breast Radiotherapy by Anatomical Measurements Before Treatment Planning

OBJECTIVE To evaluate the predictive value of the patient's anatomical measurements on ipsilateral lung doses before the whole breast radiotherapy (WBRT) planning. In planning WBRT, the ipsilateral lung is a major organ at risk. Prediction of lung doses can be helpful to choose the RT technique. METHODS Thoracic diameters, length and volume of the breast and ipsilateral lung, the height of the contralateral breast, and distance between two breasts were measured as anatomical parameters on the RT simulation computerized tomography (CT) images. Also, the ratios and differences of thoracic diameters were calculated. The correlation between the ipsilateral lung doses and anatomical parameters were evaluated in order to specify cut-off values that can predict high lung doses. RESULTS 102 patients who undergone breast-conserving surgery+WBRT were enrolled in this study. The anterior-posterior diameter of the thorax at the level of sternal notch (AP-D-notch) and xiphisternal junction (AP-D-xiphi); the ratios of anterior-posterior and left-right diameters of the thorax (R-notch and R-xiphi); the difference between AP-D-xiphi and AP-D-notch (APDdiff) and the difference between the left-right diameters of the thorax at the level of sternal notch and xiphisternal junction (LRDdiff) were the statistically significant correlated parameters with lung doses. It can be predicted that the ipsilateral lung doses will be above average if the patients' measurements are as AP-D-notch<17.5cm, AP-D-xiphi<23.5cm, R-notch<0.91cm, R-xiphi<0.86cm, APD(diff)>1.95cm and LRDdiff<6.96cm. CONCLUSION This is the first study that is evaluating the correlation between patient's anatomical features and ipsilateral lung doses in WBRT. Measuring and calculating AP-D-notch, AP-D-xiphi, R-notch, R-xiphi, AP-D-diff and LR-D-diff on RT simulation CT images can be predictive.