Purpose: The Dual Energy Monoenergetic Algorithm (DEMA) (Siemens AG) allows for the creation of virtual monoenergetic CT images (VMIs) from dual-energy CT (DECT) scans. VMI datasets produced for 40 keV through 150 keV were evaluated to determine the dosimetric impact associated with using a predetermined VMI dataset for radiation therapy treatment planning in concert with a standard 120 kVp CT-density curve.
Methods: A Siemens SOMATOM Confidence RT Pro was used to scan an anthropomorphic phantom and a calibrated Gammex with materials ranging in density from 0.300 g cm⁻³ to 1.824 g cm⁻³. Scans were taken using a tube potential of 120 kVp. Additionally, two consecutive scans were collected for DECT with tube potentials of 80 and 140 kVp. 40 – 150 keV VMIs were created from the DECT scans. Mass density vs Hounsfield unit (HU) curves were analyzed for all Gammex scans. A VMAT treatment plan was created on the anthropomorphic phantom data sets and doses were computed and compared for the 80keV VMI and 120kVp scans.
Results: The 80 keV VMIs agreed best with the standard 120 kVp CT-density curves. For mass densities ≤ 1.340 g cm⁻³, mean HU values differed by less than 5 HU. However, for mass densities ≥ 1.560 g cm⁻³, mean HU values differed by less than 35 HU. VMAT treatment plans computed on an anthropomorphic phantom demonstrated clinically equivalent dosimetry when computed on 80keV and 120kVp scans using a common CT-density curve.
Conclusion: Dosimetric differences were found to be negligible when using an 80 keV VMI dataset for radiation therapy treatment planning with a standard 120 kVp CT-density curve. It is feasible to implement DECT for clinical radiation therapy dose calculation while using a single common CT-density curve within a treatment planning system for all CT protocols.