SU‐E‐J‐136: Investigation Into Robustness of Stopping Power Calculated by DECT and SECT for Proton Therapy Treatment Planning

Abstract

Purpose:To investigate the robustness of dual energy CT (DECT) and single energy CT (SECT) proton stopping power calibration techniques and quantify the associated errors when imaging a phantom differing in chemical composition to that used during stopping power calibration.Methods:The CIRS tissue substitute phantom was scanned in a CT‐simulator at 90kV and 140kV. This image set was used to generate a DECT proton SPR calibration based on a relationship between effective atomic number and mean excitation energy. A SECT proton SPR calibration based only on Hounsfield units (HUs) was also generated. DECT and SECT scans of a second phantom of known density and chemical composition were performed. The SPR of the second phantom was calculated with the DECT approach (SPR_DECT),the SECT approach (SPR_SECT) and finally the known density and chemical composition of the phantom (SPR_ref). The DECT and SECT image sets were imported into the Pinnacle3 research release of proton therapy treatment planning. The difference in dose when exposed to a common pencil beam distribution was investigated.Results:SPR_DECT was found to be in better agreement with SPR_ref than SPR_ SECT. The mean difference in SPR for all materials was 0.51% for DECT and 6.89% for SECT. With the exception of Teflon, SPR_DECT was found to agree with SPR_ref to within 1%. Significant differences in calculated dose were found when using the DECT image set or the SECT image set.Conclusion:The DECT calibration technique was found to be more robust to situations in which the physical properties of the test materials differed from the materials used during SPR calibration. Furthermore, it was demonstrated that the DECT and SECT SPR calibration techniques can Result in significantly different calculated dose distributions.