Experimental Study on Dual-Energy Cone-Beam CT for Proton Therapy Planning
David Leibold (TU Delft - Applied Sciences)
Marlies C. Goorden (TU Delft - Applied Sciences)
Dennis R. Schaart (TU Delft - Applied Sciences, Holland Proton Therapy Centre)
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Abstract
The objective of this study is to test the ability of dual-energy CBCT to extract proton stopping power ratio (SPR) values for proton radiotherapy planning and to compare its performance to single-energy CBCT, while optimising the operating parameters of both single- and dual-energy CBCT for SPR extraction. We scanned three phantoms with a clinical CBCT installed in the gantry of a proton therapy facility at different source voltage and current settings. Dual-energy CBCT was emulated by combining scans from different kVps. We employed the Hünemohr-Saito method to predict SPR values for dual-energy CBCT scans, whereas we used a Hounsfield look-up table for predicting SPR values based on single-energy CT scans. The optimum operating parameters for dual-energy CBCT scans were an 80/125 kVp combination with a low/high kVp dose ratio of 75/25. This resulted in a relative mean error (RME) and a relative root mean square error (RRMSE) of (0.1 ± 1.2) % and (2.53±0.73) %, respectively. For single-energy CBCT scans, 125 kVp was determined to be the optimum voltage, yielding a RME and RRMSE value of (1.5±3.3) % and (7.1±6.9) %, respectively. Although limited in scope and in need of further experiments, this study indicates that dual-energy CBCT performs better than single-energy CBCT.