Comparing the RSP Accuracy of Dual-Energy to Conventional Single-Energy CT for Potential Reduction of Clinical Safety Margins in Proton Therapy

In proton therapy, treatment planning is reliant on the accurate prediction of relative stopping power (RSP) to calculate the proton range necessary to sufficiently treat the target volume and minimize the dose given to healthy tissue and organs at risk. However, uncertainties resulting from approximations made in the calculation of RSP from CT numbers necessitates the use of 2.5%-3.5% range uncertainty margin. This study aimed to evaluate the potential reduction of this uncertainty margin using Dual-Energy CT (DECT) by comparing the RSP accuracy of an ultra-fast switching KV DECT to conventional Single- Energy CT (SECT). Reference RSP values of tissue-mimicking cylindrical plugs and fresh, postmortem lamb tissue were obtained using MLIC measurements and proton CT respectively. RSP values were then derived from DECT and SECT of both the tissue-mimicking plugs and the lamb tissue and their percentage difference from the reference RSP values was calculated. Overall, DECT demonstrated a lower mean absolute percentage error than SECT for all tissue types in both tissue mimicking phantoms and in animal tissue, potentially implying that the use of DECT could reduce uncertainty in treatment planning.