Investigation of the Effect of CT-Relative Electron Density Curves on Radiotherapy Dose Calculation

Abstract

The computerized tomography scanners play a significant role in the radiotherapy treatment planning process. The electron density obtained from the CT-RED curve can be used to determine the structure of materials, and TPS calculates the dose based on the material's composition. Errors in this curve can lead to inaccuracies in dose estimation, particularly in heterogeneous tissues. In this study, the effect of variations in the CT-RED curve on the radiation dose calculated with different algorithms was also investigated. A virtual phantom was created by the TPS system for five different environments, including two low-density (HU:-750 and HU:-300) and two high-density (HU:750 and HU:300) materials. Four different erroneous CT-RED curves were created, representing -5%, -10%, +5%, and + 10% deviations from the original CT-RED curve. The positive deviations are more prominent in regions with low HU values. On the other hand, negative errors tend to be more noticeable in regions with higher HU values. This indicates that changes in dose discrepancies are not proportional to the variations in HU. Since the HU values are converted to RED by the TPS, inconsistencies in HU values may lead to errors in the dose calculated by TPS. It is evident that errors in the CT-RED curve can affect the dose calculated by the TPS. However, it appears that this effect remains within acceptable limits. Given that different errors can combine to create significant differences, it is crucial not to overlook the importance of accurately transferring the CT-RED curve to the TPS.