Prediction of dose-volume histograms in nasopharyngeal cancer IMRT using geometric and dosimetric information.

A method using both patient geometric and dosimetric information was proposed to predict dose-volume histograms (DVHs) of organs at risk (OARs) for a nasopharyngeal cancer (NPC) intensity-modulated radiation therapy (IMRT) plan. A total of 106 nine-field IMRT NPC plans were used in this study. Twenty-six plans were randomly selected as testing cases, and the remaining plans were used as the training data. A method employing geometric and dosimetric information was developed for OAR DVH prediction. The dosimetric information was derived from an initial dose calculation using a simple unoptimized conformal plan. The DVHs were also predicted using only the geometric information. The DVH prediction model was a generalized regression neural network (GRNN). Mean absolute error (MAE) and R 2 values were introduced to evaluate DVH prediction accuracy. Significant differences in the DVH prediction accuracy were found between the method employing the geometric and dosimetric information and the method utilizing the geometric information for the brainstem (R 2, 0.98 versus 0.95, p   =  0.007; MAE, 3.52% versus 7.19%, p   =  0.002), spinal cord (R 2, 0.98 versus 0.96, p   <  0.001; MAE, 2.80% versus 4.36%, p   <  0.001), left optic nerve (R 2, 0.90 versus 0.77, p   =  0.014; MAE, 3.07% versus 11.29%, p   =  0.025) and other organs. On average, the R 2 value increased by ~6.7% and the MAE value decreased by ~46.7% after adding the dosimetric information to the DVH prediction. We developed a method for predicting DVHs of OARs in NPC IMRT plans by using geometric and dosimetric information. Adding dosimetric information can help predict the DVHs of OARs in NPC IMRT plans.