A study to determine the least susceptible planning technique to proton dose computation error in pseudo CT

This is to study and determine IMPT planning technique, which has least susceptibility to CT number approximation of Pseudo CT images based on dose computation accuracy. The dose error is mainly due to difference in the radiological distance (WET-Water Equivalent Thickness) of the data sets and error in spatial distribution of CT numbers. With the right CT to density table and CT to Stopping power table, error in radiological depth of the pseudo CT can be minimized. But the CT number geometric/spatial error is difficult to tame due to the high heterogeneity resolution of patient image data. This study shows Robust optimization with 5% range error input helps to reduce the sensitivity of dose to CT density approximation. Due to the difference in CT density distribution between CT and Pseudo CT images results in range error of spot scanning proton beams resulting in dose errors. These range errors can be minimized using robust optimization with range error margin. A combination of RO and SFUD also results in similar results but there is not enough evidence to state SFUD adds to the advantage of robust optimization